Spectrally isolated zero modes (SIZMs) play a key role in diverse areas of physics and engineering. Typically, such modes depend on the lattice symmetry and manifest as spatially localized states. Here, we propose a simple yet universal mechanism for constructing SIZMs with arbitrary spatial profiles in any lattice. By introducing a zero-energy “head” site to a generic “body” lattice via unidirectional couplings, we realize a symmetry-independent yet energetically robust SIZM distributed over the body lattice. More importantly, we can precisely customize the spatial morphology of the SIZM, including not only its amplitude distribution but also its phase pattern, by flexibly tailoring the unidirectional couplings. Experimentally, we demonstrate this framework in our reconfigurable acoustic platform, showcasing diverse zero-mode morphologies across one-dimensional and two-dimensional systems. All experimental data show excellent agreement with simulations. Our work establishes a versatile and powerful paradigm for designing and controlling SIZMs, with promising applications across multidisciplinary fields.

Most materials with high thermal conductivity belong to one of two classes: metals, where heat is carried predominantly by electrons, and insulators, where heat transport is dominated by the phonon contribution. Materials that combine substantial electronic thermal conductivity and lattice thermal conductivity are rare, because the mechanisms that favor electron transport typically suppress phonon transport, and vice versa. Here, we report the theoretical prediction and experimental realization of such a material, metallic $\varepsilon$-TaN. Our calculations predict a total thermal conductivity at room temperature of $273\pm 5\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ in single crystals and $145\pm 5\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ in polycrystals with $0.5\mu \mathrm{m}$ grains, with an unusually large lattice contribution (79%) for a metal. The latter value is in agreement with our local transient thermoreflectance measurements on polycrystalline samples yielding $\sim 130\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$. We show that the balanced electronic and lattice thermal conductivities of $\varepsilon$-TaN originate from a combination of large Fermi velocity and small Fermi density of states on the electron side, and large speed of sound and wide phonon gap on the lattice side.

The interaction between the electrons and the lattice vibrations in a solid is responsible for various important effects, such as formation of polarons, temperature-dependent band gaps, phonon-limited carrier transport, and conventional superconductivity. Most works assume a linear electron-phonon interaction, where the electron only interacts with one phonon at a time. However, the validity of this assumption has not been verified in polar anharmonic materials, where large ionic displacements may invalidate the assumption of linear interaction. Here, we show that nonlinear electron-phonon interactions contribute significantly to the finite-temperature electron mobility of the inorganic lead halide perovskite ${\mathrm{CsPbI}}_3$. The effect of nonlinear interaction is taken into account using the recently derived expression for the long-range part of the one-electron-two-phonon matrix element. We calculate the electron mobility from first principles within the self-energy relaxation-time approximation, treating the electron-phonon coupling in the long-range approximation. Despite these approximations, the calculated mobilities are in good agreement with the available experimental data, while enabling us to isolate and quantify the contribution of nonlinear electron-phonon interactions relative to the conventional linear coupling. We find that the one-electron-two-phonon interaction modifies the temperature dependence of the mobility in ${\mathrm{CsPbI}}_3$ and reduces its room-temperature value by about 10%. This sizable contribution results from the combined effects of strong lattice anharmonicity and large thermal phonon populations, the latter being enhanced by the low phonon frequencies associated with the heavy constituent atoms. These results identify a regime in which nonlinear electron-phonon interactions become relevant and indicate that they should be explicitly considered for finite-temperature properties of anharmonic halide perovskites.

We studied acoustoelectric (AE) currents in materials that undergo charge density wave (CDW) transitions, induced by a surface acoustic wave (SAW) on a piezoelectric substrate. The polarity and magnitude of the AE current in ${\mathrm{NbSe}}_3$ and $2H\text{−}{\mathrm{TaSe}}_2$ were modulated due to their CDW transitions. We also found that the sign of the AE current depends on the SAW propagation direction with respect to the crystalline axis of the substrate. A phenomenological model assuming strain-modified conductivity can qualitatively account for the significant modulation of the AE current associated with the CDW transition, as well as the SAW propagation orientation dependence. The present results offer a powerful probe for exploring SAW-electron interactions in van der Waals materials, thereby highlighting their potential for advancing the emerging field of straintronics.

Thouless pumping is a transport phenomenon whereby an insulating, time-periodic Hamiltonian induces a robustly quantized transfer of charge, per driving cycle, in the quasiadiabatic limit. In this work, we apply the shortcuts to adiabaticity method of counterdiabatic (CD) driving to the Rice-Mele model, an archetypal model for Thouless pumping. We show that the charge pumped rapidly across each bond of our CD Rice-Mele model is robustly quantized and determined by a Chern number. The CD Hamiltonian generally involves long-range, hence nonlocal, hopping. Therefore we also derive an exact, local, nearest-neighbor CD Hamiltonian for our lattice system. We show that our nearest-neighbor nonadiabatic protocol possesses the same topological robustness to on-site disorder as quasiadiabatic Thouless pumps and is moreover surprisingly robust to on-site disorder and noise errors in implementing the CD protocol for sufficiently rapid driving. The protocol also reproduces finite-temperature Thouless pump results away from the adiabatic limit. In addition, we develop a general method to produce nontrivial, finite-time quantized pumping starting from any Rice-Mele initial ground state using only nearest-neighbor hopping.

In an ultrafast optical-pump terahertz-probe measurement, the photoinduced material response can be modulated on a timescale shorter than the extent of the THz pulse. In this situation, the measured time-frequency response deviates from a simple time-dependent linear response. When full two-dimensional time-frequency maps are measured, oscillatory artifacts persisting after pump-probe overlap can be incorrectly assigned to a photoexcited coherent response. We investigate this experimentally via the measured response of photoexcited SnSe, whereby photoinduced phase change dynamics lead to ultrafast changes of the charge carrier and lattice optical conductivity. Two-dimensional time-frequency THz transmission maps subsequently show unexpected time-frequency features at early pump-probe delay times. These features are reproduced in both finite-difference time-domain simulations of the THz experiment and in an extension of non-equilibrium response function theory, demonstrating their systematic origin.

The microsopic origin of the charge-density wave (CDW) in $A{\mathrm{V}}_3{\mathrm{Sb}}_5$ ($A$ = K, Rb, Cs) kagome metals remains a longstanding question, often revolving around electron-phonon coupling and purely electronic mechanisms involving Van Hove scenarios, nesting, and sublattice interference. To reveal the processes driving the CDW transition, we combine ab initio calculations analysis of the phonon self-energy and ARPES. Our momentum-resolved study, supported by ARPES data, reveals that lattice instabilities in the V-135 family of kagome metals appear to also be driven by electronic states far from high-symmetry points, where these states exhibit the strongest coupling with the phonon modes responsible for the CDW distortion. Footing on an interpretation scheme based on phonon fluctuation diagnostics, our work challenges and revises theories that so far have exclusively attributed CDW formation to nesting effects close to the Fermi level.

Single-crystal tellurium provides an elemental platform for examining how electron-phonon coupling and anharmonic phonon scattering appear in Raman spectra and lattice thermal transport. Here, we combine temperature-dependent Raman spectroscopy with first-principles calculations to investigate the phonon response and heat transport of trigonal Te. The calculated electronic structures are strongly modified by spin-orbit coupling, whereas the phonon spectra obtained with and without spin-orbit coupling show only minor differences. Raman measurements reveal a pronounced Fano asymmetry of the $A_1$ mode at low temperature, indicating interference between a discrete phonon and an electronic continuum. The inverse asymmetry parameter $1/q$ decreases toward the Lorentzian limit upon warming, showing that the Fano interference becomes less pronounced at elevated temperatures. Mode-resolved frozen-phonon calculations show that the in-plane $E^1$ and $A_1$ displacements produce appreciable phonon-induced electronic band responses near the $H$ point, where the low-energy bands have strong $p_x/p_y$ character, whereas the $E^2$ displacement produces a weaker response. The temperature-dependent Raman shifts and linewidths are described within a Balkanski-type anharmonic framework, with the linewidths indicating appreciable higher-order anharmonic contributions for selected optical modes. First-principles thermal-transport calculations further show that four-phonon scattering shortens the lifetimes of low-frequency heat-carrying phonons and reduces the lattice thermal conductivity. These results clarify the distinct roles of the mode-selective Fano response and anharmonic phonon scattering in the Raman spectra and lattice thermal transport of single-crystal Te.

Over the past decades, high harmonic spectroscopy (HHS) has emerged as a powerful tool for all-optical probing of topological properties of solids. There are outstanding questions regarding the universal nature of the spectral features of harmonics and their relationship to the nontrivial topological properties. Here, we present a systematic theoretical study of HHS in topological materials, including lower-order and higher-order topological insulators (LOTIs and HOTIs), focusing on observables such as helicity, circular dichroism, ellipticity dependence, and channel-resolved intensity yields. Using the Haldane, Kane-Mele, and breathing kagome lattice models, we theoretically extend all-optical approaches from the LOTI to the HOTI regime by explicitly incorporating contributions from bulk, edge, and corner states. Depending on the crystalline system, our calculations suggest that these observables can encode topological information through distinct modifications of the HHG spectra in topological phases. In particular, we identify significant enhancements of the harmonic intensity yields, reaching up to two orders of magnitude relative to trivial phases, together with distinct spectral signatures associated with edge and corner contributions revealed through channel-resolved intensity yields. These results show that channel-resolved HHS provides a promising route for probing topological states in both LOTIs and HOTIs.

Electron-phonon coupling has been a central topic in condensed matter physics for decades, and first-principles methods have demonstrated remarkable success in quantitatively capturing its role in a wide variety of physical phenomena and materials. Conventional calculations of electron-phonon coupling typically assume that phonons have infinite lifetimes, but phonons can exhibit finite lifetimes due to anharmonic phonon-phonon interactions. In this work, we derive an expression for the electron-phonon coupling scattering rates including the effects of anharmonic three-phonon interactions, which lead to phonon dephasing and finite phonon lifetimes. We also describe a first-principles implementation of this anharmonic electron-phonon coupling which can be seamlessly integrated within existing workflows for the evaluation of electron-phonon and phonon-phonon coupling interactions. Finally, we present calculations of electron-phonon scattering rates including phonon dephasing in a range of materials, and discuss the different microscopic mechanisms by which anharmonic phonons influence electron-phonon coupling. This study establishes the importance of finite phonon lifetimes in the evaluation of electron-phonon coupling, and provides a platform to explore these effects in a wide range of materials and phenomena.

The electron-phonon interaction underpins many material properties, for example, the conductivity of metals and the optoelectronic response of semiconductors. First-principles calculations of the electron-phonon interaction are a powerful tool to quantitatively describe many of these properties in increasingly complex materials. However, one key assumption of all calculations is that phonons have infinite lifetimes, an approximation that may break down when anharmonic phonon-phonon interactions are strong. In this work, we present a theory for the interaction of electrons with finite-lifetime phonons experiencing dephasing. Using a first-principles implementation of the theory, we find that anharmonic dephasing dramatically enhances electron-phonon scattering rates in metallic ${\mathrm{MgB}}_2$. Microscopically, phonon-phonon interactions create new scattering channels that increase the phase space available for electron-phonon scattering. As a result, anharmonic dephasing strongly suppresses conductivity in ${\mathrm{MgB}}_2$, bringing the calculated values substantially closer to experiment within the Boltzmann transport equation framework. This example establishes the importance of finite phonon lifetimes in the evaluation of electron-phonon scattering, and the microscopic mechanism suggests that anharmonic dephasing could play an important role in the conductivity of many metals. More broadly, our theory and first-principles implementation of anharmonic dephasing in the electron-phonon interaction provides a solid foundation to explore this regime in other materials.

Revealing the mechanisms of phonon scattering is crucial for understanding material properties such as transport characteristics and optical responses. It can be discussed by measuring the temperature dependence of the phonon energy and lifetime. To gain insight into these mechanisms in the Weyl semimetal $T_d\text{−}{\mathrm{WTe}}_2$, we investigated coherent phonons using time-resolved pump-probe spectroscopy in a wide temperature range from 4.6 to 300 K. The temperature dependence of the frequency and decay rate of the two high-frequency optical modes was described by the conventional anharmonic phonon-phonon scattering model. In contrast, the low-frequency mode at 2.4 THz exhibited anomalous behavior, which can be interpreted as the contribution of phonon-electron scattering.

Zitterbewegung plays a major role in electron dynamics in solids, yet is not captured in conventional semiclassical treatments. Here, starting from the quantum Liouville equation, I identify a Zitterbewegung velocity, which involves the symmetric and antisymmetric components of the quantum geometric tensor oscillating out of phase. The Zitterbewegung velocity resolves the position-shift paradox, recovering the field-induced shift in an electron's position by integrating the semiclassical equations, and is directly related to the famous minimum conductivity of massless Dirac fermions.

We present a non-Markovian theory of muon spin relaxation that treats the implanted muon as an open quantum spin coupled to a temporally correlated local magnetic environment. Using a Schwinger-Keldysh influence-functional formulation, we derive a stochastic equation of motion for the muon spin in which the fluctuation kernel is fixed by the local-field correlation tensor, while the retarded memory torque describes an effective environmental backaction. This formulation extends conventional Markovian and strong-collision descriptions to complex magnetic environments where quasistatic broadening, ion-driven colored field fluctuations, and unresolved retarded environmental response coexist and cannot be reduced to a single local-field renewal process. Within the established limits, the theory reduces to standard Kubo-Toyabe forms. This unified framework enables quantitative global analysis of zero-field and weak longitudinal-field $\mu \mathrm{SR}$ spectra, providing a consistent description of field-dependent line shapes with single parameter set at each temperature. Applied to ${\mathrm{Li}}_{0.73}{\mathrm{CoO}}_2$, the model captures the interplay between quenched Gaussian width and a Li-driven dynamical component yielding fluctuation rates consistent with activated behavior. The fitted memory parameter is most visible in the crossover between quasistatic and fast-fluctuation limits, providing a systematic basis for modeling ion-driven magnetic fluctuations in functional materials.

Periodically driven systems host topological phases without static analogs, such as the anomalous Floquet phase characterized by trivial bulk bands yet robust boundary modes. In this work, we investigate the scattering problem of a Floquet Chern insulator and reveal the non-Hermitian skin effect (NHSE) of reflected waves. Using a discrete-time scattering formalism, we demonstrate how the non-Hermitian winding number of the reflection matrix is linked to the bulk Floquet invariant via boundary resonances. This reflected-wave NHSE relies on which quasienergy gap the incident wave resides in, leading to a gap-dependent Goos-Hänchen (GH) shift. We further show that the momentum-integrated GH shift quantitatively yields the Floquet topological invariant of the corresponding gap. Our work highlights a frequency-dependent NHSE of reflected waves in driven systems and provides a real-space scattering approach to identify nonequilibrium topology.

Measurement-induced phase transitions have largely been explored for projective or continuous measurements of Hermitian observables, assuming perfect detection without information loss. Yet such transitions also arise in more general settings, including quantum-jump processes with non-Hermitian jump operators, and under inefficient detection. A theoretical framework for treating these broader scenarios has been missing. Here we develop a comprehensive replica Keldysh field theory for general quantum-jump processes in both bosonic and fermionic systems. Our formalism provides a unified description of pure-state quantum trajectories under efficient detection and mixed-state dynamics emerging from inefficient monitoring, with deterministic Lindbladian evolution appearing as a limiting case. It thus establishes a direct connection between phase transitions in nonequilibrium steady states of driven open quantum matter and in measurement-induced dynamics. As an application, we study imbalanced and inefficient fermion counting in a one-dimensional lattice system: monitored gain and loss of fermions occurring at different rates, with a fraction of gain and loss jumps undetected. For imbalanced but efficient counting, we recover the qualitative picture of the balanced case: entanglement obeys an area law for any nonzero jump rate, with an extended quantum-critical regime emerging between two parametrically separated length scales. Inefficient detection introduces a finite correlation length beyond which entanglement, as quantified by the fermionic logarithmic negativity, obeys an area law, while the subsystem entropy shows volume-law scaling. Numerical simulations support our analytical findings. Our results offer a general and versatile theoretical foundation for studying measurement-induced phenomena across a wide class of monitored and open quantum systems.

Many-body chaos is a default property of many-body systems; at the same time, near-integrable behavior due to weakly interacting quasiparticles is ubiquitous throughout condensed matter at low temperature. There must therefore be a, possibly generic, crossover between these very different regimes. Here, we develop a theory encapsulating the notion of a cascade of lightcones seeded by sequences of scattering of weakly interacting harmonic modes as witnessed by a suitably defined chaos diagnostic (classical decorrelator) that measures the spatiotemporal profile of many-body chaos. Our numerics deals with the concrete prototypical case of a classical Heisenberg chain, for either sign of the interaction, at low temperatures where the short-time dynamics are well captured in terms of noninteracting spin waves—characteristic to continuous symmetry breaking. To model low-temperature dynamics, we use ensembles of initial states with randomly embedded point defects in an ordered background, which provides a controlled setting for studying the scattering events. The decorrelator exhibits a short-time integrable regime followed by an intermediate “scarred” regime of the cascade of lightcones in progress; these then overlap, leading to an avalanche of scattering events which finally yields the standard long-time signature of many-body chaos.

The study of real-time dynamics of fermions remains one of the last frontiers beyond the reach of classical simulations and is key to our understanding of quantum behavior in chemistry and materials, with implications for quantum technology. Here we present a Heisenberg-picture algorithm that propagates observables expressed in a Majorana-string basis using a truncation scheme that preserves Trotter accuracy. The framework is exact for quadratic Hamiltonians, where it remains restricted to a fixed low-weight sector determined by the physical observable, it admits variational initial states, and extends to interacting regimes via systematically controlled truncations. We benchmark our approach on one- and two-dimensional Fermi-Hubbard quenches, comparing against tensor network methods and recent experimental data. The method achieves high accuracy on timescales comparable to state-of-the-art variational techniques and experiments, demonstrating that controlled Majorana-string truncation is a practical tool for simulating two-dimensional fermionic dynamics.

At a generic volume- to area-law entanglement transition in a many-body system, quantum chaos is arrested. We argue that this tends to imply the vanishing of a certain “mass” term in the field theory of the measurement-induced phase transition (MIPT) for monitored, interacting fermions. To explore this idea, we consider the MIPT with no conserved quantities that describes one-dimensional monitored, interacting Majorana fermions in class DIII. This is the most general problem of interacting fermions with weak fermion parity measurements. Without interactions, it is known that a noninteracting MIPT separates the area-law phase from a log-enhanced “thermal metal” phase at sufficiently weak monitoring. We conjecture that the MIPT with interactions is the same as the noninteracting one in this case; the volume-law phase arises through the dangerously irrelevant mass. The physical picture is that the mass represents a local Fermi's golden rule interparticle scattering rate density that is tantamount to the entangling rate density. The latter must vanish continuously at a continuous MIPT. On the other hand, the field theory capturing the MIPT for monitored fermions with additional continuous symmetries is expected to be different, because the interactions introduce additional terms associated to conserved Noether currents. We propose numerical tests of our conjecture. In addition, we analytically identify a candidate noninteracting critical point representing the MIPT, using a controlled $\varepsilon$-expansion.

We present an exact solution for entanglement entropy for the real-time dynamics following a quench from a thermal pure quantum (TPQ) state in a free-fermion system. In contrast to the usual linear growth and saturation behavior, the entanglement entropy exhibits a characteristic double-plateau structure. We establish this behavior through three complementary approaches: an exact conformal field theory calculation on the Klein bottle, finite-size Gaussian-state simulations, and a quasiparticle picture that becomes quantitatively accurate in the scaling regime.