Heat transport in bulk materials is well described using the Debye theory of three-dimensional vibrational modes (phonons) and the acoustic match model. However, in cryogenic nanodevices, phonon wavelengths exceed device dimensions, leading to confinement effects that standard models fail to address. With the growing application of low-temperature devices in communication, sensing, and quantum technologies, there is an urgent need for models that accurately describe heat transport under confinement. We introduce a computational approach to obtain phonon heat capacity and heat transport rates between solids in various confined geometries that can be easily integrated into, e.g., the standard two-temperature model. Confinement significantly reduces heat capacity and may slow down heat transport. We validate our model with experiments on strongly disordered NbTiN superconducting nanostructure, widely used in highly efficient single-photon detectors, and we argue that confinement is due to their polycrystalline granular structure. These findings point to potential advances in cryogenic device performance through tailored material and microstructure engineering.

It has been recently proposed that a fully gapped $d$-wave superconducting phase emerges in twisted bilayer cuprates when twist angle is in the vicinity of ${45}^{\circ }$. By considering a twisted bilayer model with a moiré cell, we study the local electronic structure around a single-site impurity and impurity dimer in both topologically trivial and nontrivial superconducting states. We find that the topological nontrivial superconducting phase is robust against single scalar-potential impurity scattering but is very sensitive to the interlayer impurity dimer scattering, which avoids and enforces the creation of the subgap quasiparticle state. This behavior is intrinsic to the bilayer structure and topological nature, in contrast to the other types of impurities that inevitably bring subgap quasiparticle states. We expect that our results can contribute to the understanding of electronic properties of twisted bilayer cuprates systems.

Understanding non-equilibrium melting in metals is a topic of current interest. We investigated the solid-to-liquid phase transition in platinum induced by femtosecond infrared radiation at different fluences. The evolution of the atomic structure was probed on the picoseconds timescale by x rays generated by an x-ray free-electron laser (XFEL). To analyze scattering data, we employed a model developed for liquid metals. We observed a compression field propagating into the nanostructured thin film sample, as well as partial melting for the infrared fluence of $200\mathrm{mJ}{\mathrm{cm}}^{-2}$, corresponding to about $280\mathrm{kJ}{\mathrm{kg}}^{-1}$ absorbed by the sample. Similar features were observed at higher infrared laser fluences. To support the interpretation of experimental findings, we performed two-temperature model simulations.

We report a new method to tailor the entire two-dimensional (2D) dispersion relation based on nonlocal phononic crystals, where beyond-nearest-neighbor (BNN) interactions are used to achieve precise sculpting of the band surface. Focusing on square lattices, we demonstrate unconventional band structures such as multifold symmetries, roton/maxon/saddle-type critical points, anisotropy-to-isotropy transitions, and other exotic band morphologies. We anticipate that the design protocols in this study can be extended to all other two-dimensional lattices and multiband customization.

The skin effect, characterized by the tendency of particles to accumulate at the boundaries, has been extensively studied in non-Hermitian systems. In this paper, we propose an intuitive Lindbladian composed of two chains with reversed skin localization. The skin steady state is gradually delocalized as the interchain coupling increases. In the single-body scenario, it corresponds to a shift in the scaling of the Liouvillian gap $\mathrm{\Delta }$ from $\mathrm{\Delta }\propto N^0$ to $\mathrm{\Delta }\propto N^{-2}$. Notably, exact diagonalization results reveal a system-size sensitivity of the single-particle Liouvillian spectrum, inherited from the system-size sensitivity of the non-Hermitian effective Hamiltonian. We predict that even an arbitrarily small coupling will induce dramatic changes in the Liouvillian spectrum and steady state in the thermodynamic limit, a phenomenon we term the critical Liouvillian skin effect. Additionally, in the many-body scenario, by employing the stochastic Schrödinger equation to unravel the Lindblad master equation, it is revealed that the scaling behavior of steady-state entanglement changes from the area law to the logarithmic law. In this paper, we demonstrate the delocalization of both single- and many-body skin steady states, introducing a mechanism for inducing entanglement transitions beyond the quantum Zeno effect.

Pressure-dependent synchrotron x-ray diffraction (XRD), nuclear resonant inelastic x-ray scattering (NRIXS), and nuclear forward scattering (NFS) measurements were made on ${}^{57}\mathrm{Fe}_{55}{\mathrm{Ni}}_{45}$. XRD measurements were at 298 and 392 K at pressures up to 20 GPa, confirming a pressure-induced Invar effect between 7 and 13 GPa. A decrease of the ${}^{57}\mathrm{Fe}$ magnetic moment was found in NFS measurements under pressure, showing an increase in magnetic entropy. The ${}^{57}\mathrm{Fe}$ phonon density of states (DOS) was obtained from NRIXS measurements. The low thermal expansion in the high-pressure Invar region originates from a competition between the thermal expansion from spins and phonons as calculated from Maxwell relations. The longitudinal phonon modes changed their pressure dependence near the Curie transition, which is evidence for a spin-phonon interaction.

We present the magnetic behavior and resulting transport properties of ${\mathrm{TaSe}}_2$ when intercalated by magnetically active cobalt cations. Acting as the layered host, ${\mathrm{TaSe}}_2$ is a transition metal dichalcogenide (TMD) that adopts the $2H$-polytype. We find through our single crystal and powder diffraction studies that we can prepare the stoichiometry ${\text{Co}}_{1/4}{\text{TaSe}}_2$, which crystallizes in the centrosymmetric space group $P{6}_3/mmc$. From magnetic susceptibility and x-ray photoelectron spectroscopy measurements, we find a transition consistent with antiferromagnetic order below the temperature $T_N=173\mathrm{K}$ and ${\mathrm{Co}}^{2+}$ in the high-spin state. Neutron powder diffraction and specific heat measurements, however, point to a much smaller than anticipated ordered moment in this sample. From the neutron results, the magnetic structure can be described as an $A$-type antiferromagnet with an ordered moment size of 1.35(11) ${\mu }_B$ per Co cation. The direction of the moments is all long the $c$ axis, which is consistent with the magnetization and susceptibility studies showing this direction to be the easy axis. Interestingly, we find that a weak and subtle ferromagnetic component appears to exist along the $ab$ plane of the ${\text{Co}}_{1/4}{\text{TaSe}}_2$ crystals. We place the results of this work in the context of other magnetic-ion intercalated TMDs, especially those of Ta and Nb.

The crystal structure and magnetic property have been comprehensively investigated for single crystals of the trigonal ${\mathrm{Mg}}_2{\mathrm{Ni}}_2{\mathrm{Ta}}_2{\mathrm{O}}_9$ through x-ray diffraction (XRD), dc susceptibility, specific heat, ac susceptibility, magnetic relaxation, and magnetic memory effect measurements. Rietveld refinement of XRD data reveals the two inequivalent ${\mathrm{Ni}}^{2+}/{\mathrm{Mg}}^{2+}$ ions form the quasi-two-dimensional buckled honeycomb lattice. The dc susceptibility measurements manifest the anisotropic spin glass (SG) behavior and further confirmed by the specific heat and ac susceptibility measurements. The frequency dependency of the freezing temperature is also examined using dynamic scaling laws, including power law and Vogel-Fulcher (VF) law. The fitting from the power law yields a critical exponent $z\upsilon {}^{\prime }=8.9\pm 0.2$ and a single spin flip ${\tau }_0\simeq$ 4.35 $\times {10}^{-10}$ s. While the derived fitting parameters from the VF law are activation energy $E_a/k_B\simeq 16.4$ K and VF temperature $T_0\simeq 3.0$ K. The values of ${\tau }_0$ and a nonzero value of $T_0$ suggest the cluster SG behavior. A careful examination of nonequilibrium dynamics utilizing relaxation and memory effect experiments illustrates the progression of the system through various intermediate metastable states and notable memory effects. These aforementioned results indicate that ${\mathrm{Mg}}_2{\mathrm{Ni}}_2{\mathrm{Ta}}_2{\mathrm{O}}_9$ possesses an interesting SG state, which is induced by magnetic frustration arising from competing antiferromagnetic and ferromagnetic interactions, as well as ${\mathrm{Ni}}^{2+}/{\mathrm{Mg}}^{2+}$ ions site disorder.

We conduct local magnetic measurements on superconducting thin-film samples of ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ using scanning superconducting quantum interference device (SQUID) susceptometry. From the diamagnetic response, we extract the magnetic penetration depth, $\lambda$, which exhibits a quadratic temperature dependence at low temperatures. In high-purity bulk samples, a similar quadratic temperature dependence has been attributed to nonlocal electrodynamics. Although we cannot exclude nonlocal effects, our analysis indicates that in our thin-film samples the presence of scattering is sufficient to explain the temperature dependence of $\lambda$. While we observe micron-scale variations in the diamagnetic response and superconducting transition temperature, the form of the temperature dependence of $\lambda$ is independent of position. The growth and local characterization of superconducting thin-film ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ samples demonstrated here is a first step toward device-based tests of the superconducting order parameter in ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$.

We present a systematic study of the interaction, doping, and layer dependence of the $d_{x^2-y^2}$-wave pairing susceptibility of the Hubbard model for a stacked 2D square lattice. We perform a multi-index perturbative expansion up to fourth order to obtain coefficients in powers of the Hubbard $U$, the interlayer $V$, and the pair-hopping $J$ interactions. We evaluate the vertex diagrams that contribute to the pairing susceptibility for $\ell =2,3,4$ layered models in the $U\text{−}V\text{−}J$ interaction space. This provides unprecedented access to the pairing amplitudes, allowing us to identify the processes that enhance or reduce pairing. We distinguish pairing within the diagonal channel, $P_d^{\parallel }$, and off-diagonal channel, $P_d^{\perp }$, and find that, in the absence of $J$, the qualitative behavior of the layered system is equivalent to the single-layer model. In the presence of $J$, we show that pairing is enhanced sublinearly with increasing $\ell$ and is primarily mediated by the $P_d^{\perp }$ component and find which coefficients and diagram sets are responsible. Finally, we construct a generalized $\ell$-dependent equation for $P_d^{\perp }$ to speculate pairing beyond $\ell =4$.

We present a comprehensive ab initio study of superconductivity in NbTi, the workhorse for many applications. Despite being a “textbook” material, NbTi turns out to be a major challenge for computational superconductivity. In fact, anharmonic effects are crucial to obtain dynamically stable phonons for the ordered bcc phase, unstable at the harmonic level, and beyond-Morel-Anderson effects in the Coulomb interaction reduce the $T_c$ by more than 20%. Lattice disorder causes an additional large discrepancy in $T_c$ compared to experiment. Our results imply that a quantitative description of technologically relevant superconductors requires methodological developments beyond the current standards.

We propose a dissipative phase transition in a head-to-tail Bose Josephson junction. The quantum phase transition has the same origin as the one in a resistively shunted Josephson junction, but the intrinsic momentum coupling between the Josephson mode and the bath modes enables us to observe the dissipative phase transition without any synthetic dissipation. We show that the interatomic interaction strength plays the role of the damping parameter. Consequently, in contrast to a resistively shunted Josephson circuit, the Bose Josephson junction can exhibit an insulating phase in a wider parameter region by increasing the repulsive interaction strength, which is robust against nonperturbative effects. We argue that tight transverse confinement of the quasi-one-dimensional atomic gas allows us to reach the insulating phase.

In this paper, we investigate the in-plane angular and temperature dependence of coercivity and exchange bias in a ${\mathrm{V}}_2{\mathrm{O}}_3/\mathrm{Ni}$ magnetic bilayer structure, grown on an $r$-plane sapphire ($\alpha \text{−}{\mathrm{Al}}_2{\mathrm{O}}_3$) substrate using reactive dc-magnetron sputtering. Distinct variations are observed in coercivity and exchange field across the structural phase transition in ${\mathrm{V}}_2{\mathrm{O}}_3$, depending on in-plane angles and different field cooling states, as well as the direction of the applied cooling field. A peak in coercivity, occurring at a temperature corresponding to the phase coexistence region of the ${\mathrm{V}}_2{\mathrm{O}}_3$ structural transition, is observed only along the primary easy axis ($0^{\circ }/{180}^{\circ }$) of the film, disappearing at other angles and remaining independent of the field cooling state. Temperature-dependent measurements, with the applied cooling field along different angles, revealed that the onset of exchange bias at the structural phase transition of the ${\mathrm{V}}_2{\mathrm{O}}_3$ occurs irrespective of the cooling field state, yet demonstrates a complex in-plane angular dependence based on the orientation of the applied cooling field. The cooling field orientation influences the exchange bias's anisotropy, magnitude, and direction; notably, a typical unidirectional symmetry emerges when the cooling field aligns with the secondary easy axis (${90}^{\circ }/{270}^{\circ }$) of the film, which nearly aligns with vanadium magnetic moments.

Harnessing the Spin-orbit coupling (SOC) driven manifestations in electronic structure for device application comprises one of the challenging fields in spintronics application. One such avenue to achieve this is via Rashba-Dresselhaus (RD) effect, which leads to the splitting of spin states at the band edges in momentum space enabling the creation of separate spin channels for spin current control. In some multifunctional perovskite materials, the RD effect coexists with ferroelectricity, where ferroelectric (FE) phase transitions can induce spin chirality reversal, presenting opportunities for spin-FET development. We explore the effect of A cation (A= K, Rb, Cs, Tl) in spin-FET application of ${\mathrm{AIO}}_3$ compounds via investigating the RD effect and FE properties. Our results demonstrate that smaller A-cation size leads to higher RD spin splitting, with ${\mathrm{KIO}}_3$ exhibiting the most promising performance. Out of the four compounds studied, three of them show RD spin splitting $\ge$ 1 eVÅ at the conduction band. Furthermore, we observe that FE phase transitions in all these compounds can influence the spin chirality. The FE switching barriers of all four compounds are below 1 eV/atom. ${\mathrm{KIO}}_3$ has the lowest barrier of 193 meV/atom. These findings highlight the potential of ${\mathrm{AIO}}_3$ compounds for spin-FET applications and suggest avenues for further optimization.

Universal critical properties can manifest themselves not only in spatial but also in temporal directions. It has been found that critical point with emergent symmetry exhibits intriguing spatial critical properties characterized by two divergent length scales, attracting long-term investigations. However, how the temporal critical properties are affected by emergent symmetry is largely unknown. Here, we study the nonequilibrium critical dynamics in the three-dimensional ($3\mathrm{D}$) clock model, whose critical point has emergent $U\left(1\right)$ symmetry. We find that in contrast to the magnetization $M$, whose relaxation process is described by the usual dynamic exponent $z$ of the $3\mathrm{D}$ XY universality class, the angular order parameter ${\varphi }_q$ shows a remarkable two-stage evolution characterized by different dynamic critical exponents. While in the short-time stage the relaxation dynamics is governed by $z$, in the long-time stage the dynamics is controlled by a new dynamic exponent $z^{\prime }$. Further scaling analyses confirm that $z^{\prime }$ is an indispensable dynamic critical exponent. Our results may be detected in the hexagonal $R{\mathrm{MnO}}_3$ ($R=\mathrm{rare}$ earth) materials experimentally.

We present a detailed investigation of the XXZ Heisenberg model for spin-$1/2$ and spin-1 systems on square and honeycomb lattices. Utilizing the density-matrix renormalization group method, complemented by spiral boundary conditions (SBCs) for mapping two-dimensional (2D) clusters onto one-dimensional chains, we meticulously explore the evolution of staggered magnetization and spin gaps across a broad spectrum of easy-axis anisotropies. Our study reveals that despite the lower site coordination number of the honeycomb lattice, which intuitively suggests increased quantum fluctuations in its Néel phase compared to the square lattice, the staggered magnetization in the honeycomb structure exhibits only a marginal reduction. Furthermore, our analysis demonstrates that the dependence of staggered magnetization on the XXZ anisotropy $\mathrm{\Delta }$, except in close proximity to $\mathrm{\Delta }=1$, aligns with series expansion predictions up to the 12th order. Notably, for the $S=1/2$ honeycomb lattice, deviations from the 10th-order series expansion predictions near the isotropic Heisenberg limit emphasize the critical influence of quantum fluctuations on the spin excitation in its Néel state. Additionally, our findings are numerically consistent with the singular behavior of the spin gap near the isotropic Heisenberg limit as forecasted by spin-wave theory. The successful implementation of SBCs marks a methodological advancement, streamlining the computational complexity involved in analyzing 2D models and paving the way for more precise determinations of physical properties in complex lattice systems.

Magnetic systems can exhibit thermally activated transitions whose timescales are often described by an Arrhenius law. However, robust predictions of such timescales are only available for certain cases. Inspired by the harmonic theory of Langer, we derive a general activation rate for multidimensional spin systems. Assuming local thermal equilibrium in the initial minimum and deriving an expression for the flow of probability density along the unstable dynamical mode at the saddle point, we obtain the expression for the activation rate that is a function of the Gilbert damping parameter, $\alpha$. We find that this expression remains valid for the physically relevant regime of $\alpha \ll 1$. When the activation is characterized by a coherent reorientation of all spins, we gain insight into the prefactor of the Arrhenius law by writing it in terms of spin wave frequencies and, for the case of a finite spin chain, obtain an expression that depends exponentially on the square of the system size indicating a break-down of the Meyer-Neldel rule.

In two-dimensional turbulence systems, the emergence of large-scale structures holds profound physical implications, particularly as it indicates the occurrence of inverse energy cascades, thereby garnering significant attention. In this paper, we report a vortex cluster formation mechanism in the background of near-extreme Reissner-Nordström black hole holographic model. At temperatures nearing absolute zero, we observe the formation of vortex clusters accompanied by the appearance of inverse energy cascade. Through a comparative analysis with the dynamics of the Gross-Pitaevskii equation, we reveal the special mechanism in holographic superfluid. Unlike typical quantum systems, the formation of holographic vortex clusters is driven by unique quantum dissipation properties, caused by filling with normal material similar to strange metallic states, as in high-temperature superconductivity, characterized by the fact that the vortex dipoles can hardly move at low temperatures. Our research demonstrates significant difference for vortex motion in strongly interacting superfluid, which provides a promising route to be observed in the strongly interacting Fermi gas experiments.

The superconducting diode effect (SDE) is a magnetoelectric phenomenon where an external magnetic field imparts a nonzero center-of-mass momentum to Cooper pairs, either facilitating or hindering the flow of supercurrent depending on its direction. We propose that quantum spin Hall insulator (QSHI)-based Josephson junctions can serve as versatile platforms for nondissipative electronics exhibiting the SDE when triggered by a phase bias and an out-of-plane magnetic field. By computing the contributions from Andreev bound states and the continuum of quasiparticle states, we provide both numerical and analytical results scrutinizing various aspects of the SDE, including its quality $Q$ factor. The maximum value of the $Q$ factor is found to be universal at low (zero) temperatures, which ties its origin to underlying topological properties that are independent of the junction's specific details. As the magnetic field increases, the SDE diminishes due to the closing of the induced superconducting gap caused by orbital effects. To observe the SDE, the QSHI-based Josephson junction must be designed so that its edges are transportwise nonequivalent. Additionally, we explore the SDE in a more exotic yet realistic scenario, where the fermionic ground-state parity of the Josephson junction remains conserved while driving a current. In this $4\pi$-periodic situation, we predict an enhancement of the SDE compared to its $2\pi$-periodic, parity-unconstrained counterpart.