We employ cryogenic scanning tunneling microscopy to observe a tunable two-dimensional electron gas (2DEG) on the $\mathrm{Sn}/\mathrm{Si}\left(111\right)\text{−}2\sqrt{3}\times 2\sqrt{3}-R{30}^{\circ }$ surface, where its properties are modulated by the underlying Si(111) substrates. The 2DEG resides near the conduction band edge of the Sn overlayer, which features a band gap of approximately 0.65 eV. By analyzing quasiparticle interference patterns induced by the 2DEG, we determine its energy dispersion and reveal a variation in effective mass with the Si substrate doping. Moreover, quantum interference fringes are found in spatially confined regions of the 2DEG, from which consistent band parameters are deduced. This study advances our understanding of the 2DEG and associated electronic properties in heterostructures.

Advanced thermal management is vital for reliable electronics, and quantum thermal transistors (QTTs) offer a novel solution using quantum mechanical states to control heat like electric current. They offer the potential to be used in thermal circuits that enhance thermal management capabilities. Despite substantial theoretical progress, practical realization faces challenges due to scalability, environmental interactions, and the influence of noise. In this work, we investigate the role of stochastic dynamics and thermal noise in QTTs through a framework based on the Heisenberg picture and quantum Langevin equations. We develop a Langevin-based model in which fluctuations in thermal baths are represented as noise, enabling a different approach to modeling system-bath interactions and energy flow in a QTT. Unlike previous approaches formulated in the Schrödinger picture, our method captures the impact of the spectral properties of the thermal baths on transistor characteristics such as energy flow variation and amplification rate. We define the heat flow in terms of system observables, offering a measurable framework for describing heat transfer. We characterize the noise spectral density of the thermal baths and analyze transistor characteristics across Ohmic, sub-Ohmic, and super-Ohmic regimes. We also demonstrate how this model extends beyond the Markovian limit, enabling exploration of non-Markovian effects. Furthermore, we show that our model recovers the Lindblad master equation bridging the Heisenberg and Schrödinger approaches. Our results highlight the importance of incorporating noise and spectral modeling to accurately describe and optimize the performance of QTTs, paving the way for more realistic device-level implementations in quantum thermal management.

The Raman scattering response of the biaxial antiferromagnet ${\mathrm{CoPS}}_3$ has been investigated as a function of both magnetic field and temperature. The peaks observed in the low-frequency spectral range $(90–200 {\mathrm{cm}}^{-1})$ have been identified as hybrid magnon-phonon excitations. The energies of the bare magnon and phonon modes and the effective coupling strengths between different excitation pairs have been determined. The strong and selective magnon-phonon interaction largely accounts for the pronounced splitting of two phononlike modes observed at 152 and 158 ${\mathrm{cm}}^{-1}$ in the antiferromagnetic phase of ${\mathrm{CoPS}}_3$. Based on the identification of bare magnon excitations and their magnetic-field dependence, we propose an updated set of parameters for the effective exchange $(J_{\mathrm{eff}}=9.9 \mathrm{meV})$ and biaxial magnetic anisotropy $(D=4.3 \mathrm{meV} \text{and} E=-0.7 \mathrm{meV})$ and advocate for an apparent anisotropic $g$ factor $({\mathrm{g}}_x\hspace{0.17em}=\hspace{0.17em}{\mathrm{g}}_y\hspace{0.17em}=\hspace{0.17em}2, {\mathrm{g}}_z=4)$ in the ${\mathrm{CoPS}}_3$ antiferromagnet.

With the shrinking of dimensionality, Coulomb interaction plays a distinct role in two-dimensional (2D) semiconductors owing to the reduced dielectric screening in the out-of-plane direction. Apart from the dielectric screening, free particles such as carriers and dipoles or excitons can also make a non-negligible contribution to the Coulomb interaction. While the Thomas-Fermi model is effective in describing charge carrier screening in three dimensions, the extent of screening resulting from neutral dipoles or excitons in both two and three dimensions remains quantitatively unclear. Here, we present an analytical solution based on linear response theory, offering a comprehensive depiction of the Coulomb screened potential from charge-neutral dipoles or excitons in both 2D and 3D systems, while the free dipole screening effect is much stronger in the 2D case than that in the 3D case. Using the derived screened Coulomb potential, we estimate the exciton binding energy shift arising from the mutual exciton screening effect, which is found to be an order of magnitude larger than that due to exchange-driven exciton-exciton interaction, yielding excellent agreement with the experimental observations. Our work provides a practical and insightful framework for directly analyzing and evaluating Coulomb interaction strength in an excitonic system in atomically thin materials, with implications for the design of electronic and optoelectronic devices.

In this work, we employ a surrogate BCS model with discrete energy levels to investigate a hybrid system comprising two quantum dots (QD1 and QD2), where QD1 is tunnel coupled to two superconducting leads, and QD2 is only tunnel coupled to QD1. Through exact diagonalization of this system, we obtain numerically exact solutions that enable rigorous computation of key physical quantities. Our analysis reveals a rich phase diagram featuring multiple controllable phase transitions mediated by quantum dot electron-electron interaction strength. Specifically, the system first undergoes an initial phase transition when tuning QD2's electron-electron interaction strength while maintaining QD1 in the noninteracting regime. Subsequent adjustment of QD1's electron-electron interaction strength induces a secondary phase transition, followed by a third transition arising from interdot electron-electron interaction modulation. Furthermore, we demonstrate that parallel magnetic field application can drive reversible ferromagnetic-antiferromagnetic phase transitions under specific parameter conditions. Finally, we report the emergence of nonlocal magnetization phenomena when subjecting QD1 to weak magnetic fields. And our results demonstrate that the orientation of nonlocal magnetization can be precisely manipulated through adjustment of the onsite interaction strength $U_2$ in QD2. Our research demonstrates significant control capabilities: we show Josephson current direction in double quantum dot Josephson junctions can be manipulated through electron-electron interaction strength modulation. Furthermore, nonlocal magnetization orientation can be switched by tuning onsite interactions within individual QD.

A robust theory of the mechanism of pair density wave (PDW) superconductivity (i.e., where Cooper pairs have nonzero center of mass momentum) remains elusive. Here we explore the triangular lattice $t\text{−}J\text{−}V$ model, a low-energy effective theory derived from the strong-coupling limit of the Holstein-Hubbard model, by large-scale variational Monte Carlo simulations. When the electron density is sufficiently low, the favored ground state is an s-wave PDW, consistent with results obtained from previous studies in this limit. Additionally, a PDW ground state with nematic d-wave pairing emerges in the intermediate range of electron densities and phonon frequencies. For these s-wave and d-wave PDWs arising in states with spontaneous breaking of time-reversal and inversion symmetries, PDW formation derives from valley-polarization and intrapocket pairing.

We have investigated the moiré Bloch bands of photoexcited electrons in image potential states on graphene covered Ir(111) surfaces using high-energy-resolution angle-resolved two-photon photoemission spectroscopy. An energy gap of approximately 20 meV at the $\overline{\mathrm{K}}$ point of the moiré Brillouin zone is resolved. The band structure is well reproduced by density functional theory (DFT) combined with the embedded Green's function technique. A simplified periodic potential model, whose spatial distribution shows close agreement with the DFT results, also describes the system well. These findings demonstrate that the electronic band structure of photoexcited states can be engineered solely via moiré potential modulation. This opens another avenue for excited-state band engineering and the design of ultrafast optoelectronic functionalities in moiré-engineered materials.

The traditional approach to quantum parameter estimation focuses on the quantum state, deriving fundamental bounds on precision through the quantum Fisher information. In most experimental settings, however, performing arbitrary quantum measurements is highly unfeasible. In open quantum systems, an alternative approach to metrology involves the measurement of stochastic currents flowing from the system to its environment. However, the present understanding of current-based metrology is mostly limited to Markovian master equations. Considering a parameter estimation problem in a two-terminal mesoscopic conductor, we identify the key elements that determine estimation precision within the Landauer-Büttiker formalism. Crucially, this approach allows us to address arbitrary coupling and temperature regimes. Furthermore, we obtain analytical results for the precision in linear-response and zero-temperature regimes. For the specific parameter estimation task that we consider, we demonstrate that the boxcar transmission function is optimal for current-based metrology in all parameter regimes.

We present Gibbs free-energy phase diagrams for compressed iron within a pressure range of 20–300 GPa and electronic temperature up to 3 eV, obtained using finite-temperature density functional and density functional perturbation theories. Our results for bcc, fcc, and hcp phases predict solid-solid phase transitions in iron driven purely by electronic entropy and temperature. We found a phase transition from hcp to bcc at pressures above 200 GPa, which depends on the electronic temperature. An experimental observation of the stability of the bcc phase above 200 GPa has recently been reported (Z. Konopkova et al., arXiv:2505.15397).

We investigate the multimagnon and the multispinon $L_3$-edge resonant inelastic x-ray scattering (RIXS) spectra of a spin-1/2 effective ${\tilde{J}}_1-{\tilde{J}}_2-{\tilde{J}}_3$ square lattice Heisenberg model in its Néel ordered phase. Motivated by the observation of satellite intensity peaks above the single magnon dispersion in the $L$-edge RIXS spectrum, we propose a resonating valence bond (RVB) inspired RIXS mechanism that incorporates the local site ultrashort core-hole lifetime (UCL) expansion. We compute the multimagnon and the multispinon excitations using $O(1/S)$ interacting spin-wave theory and Schwinger boson mean-field theory (SBMFT) formalism, respectively. We treat the x-ray scattering process up to second order in the UCL expansion. Our calculations of two-magnon, bimagnon, and three-magnon RIXS intensities reveal that interacting spin-wave theory fails to fully capture all the quantum correlations in the antiferromagnetic ordered phase. However utilizing the SBMFT framework, with a ground state that incorporates features of both the Néel order and fluctuating RVB components, we demonstrate that a RIXS bond-flipping mechanism provides an alternative deeper physical explanation of the satellite intensities. Specifically, we find that the spin-correlation spectra predicted by the fluctuating RVB mechanism aligns with higher-order UCL expansion results. We further show that the satellite intensity above the single-magnon mode can originate both from a one-to-three-magnon hybridization vertex process and from condensed spinons exhibiting Higgs mechanism. These features reflect the interplay of quantum fluctuation, entanglement, and gauge interaction effects of quantum magnetism probed by RIXS.

Magnetoelectric systems offer potential for device applications exploiting coupled states between electric and magnetic properties. Among magnetoelectric materials, ${\mathrm{Fe}}_4{\mathrm{Nb}}_2{\mathrm{O}}_9$ has attracted special attention because of its pronounced dielectric signal at high magnetic transition temperatures. However, the magnetic ground state, which is essential information for understanding its unusual magnetoelectricity, remains unclarified. Here, we report a noncollinear magnetic ground state of ${\mathrm{Fe}}_4{\mathrm{Nb}}_2{\mathrm{O}}_9$. To examine the magnetoelectric effect associated with sequential magnetic and structural transitions upon cooling, we conducted combined x-ray diffraction, magnetic susceptibility, magnetization, dielectric constant, and magnetodielectric experiments. Powder neutron diffraction experiments revealed a series of magnetic Bragg peaks and clear splitting of peaks via structural transition. Magnetic Rietveld refinements, combined with group theory analysis, determined a noncollinear antiferromagnetic structure including a significant $c$-axis moment component at 1.5 K. This study provides insights into the understanding of its magnetoelectric properties.

A ($2+1$)-dimensional superfluid in a rapidly rotating trap forms an array of vortices, with collective excitations called Tkachenko modes. Du et al. [Phys. Rev. Res. 6, L012040 (2024)] argued from an effective field theory viewpoint that these excitations are described by a field theory living on a noncommutative space. We elucidate the microscopic origin of these noncommutative fields, and present a derivation of the effective field theory for this superfluid using a lowest Landau level projected coherent state path-integral approach. Aside from conceptual clarity, this approach makes quantitative predictions about the long-wavelength, low-energy behavior in terms of the microscopic parameters of the short-range interacting lowest Landau level superfluid, relevant to trapped Bose-Einstein condensate experiments.

We study the low-energy physics of planar Josephson junction structures realized in a quasi-two-dimensional semiconductor system proximity coupled to narrow superconducting films. Using both a recursive Green's function approach and an effective Hamiltonian approximation, we investigate the topological superconducting phase predicted to emerge in this type of system. We first characterize the effects associated with varying the electrostatic potentials applied within the unproximitized semiconductor regions. We then address the problem of optimizing the width of the superconductor films and identifying the optimal regimes characterized by large topological gap values. We find that structures with narrow superconducting films of widths ranging between about 100 and $200\mathrm{nm}$ can support topological superconducting phases with gaps up to $40\%$ of the parent superconducting gap, significantly larger than those characterizing the corresponding wide-superconductor structures. This work represents the first component of a proposed comprehensive strategy to address this optimization problem in planar Josephson junction structures and realize robust topological devices.

The reduction in the yield stress of metals without excess heating under the action of pulsed, high-density electric current is called the electroplasticity effect (EPE). One explanation of the EPE is Joule heating of dislocations. Increasing the temperature of dislocation cores allows them to detach from obstacles and overcome the Peierls-Nabarro potential, while the average sample temperature changes slightly. Therefore it is important to consider a balance between Joule heating of dislocations and energy flow from heated dislocations to cooler, defect-free areas of the crystal. We address this problem numerically using a molecular dynamics simulation of a two-dimensional lattice with a random distribution of substitutional atoms of different mass and analytically using the kinetic theory (in the ballistic limit, realized for the harmonic monatomic lattice). It is found that in the ballistic case, the temperature of the dislocation core under constant heating does not increase with time due to a rapid heat flow into the crystal volume. Substitutional atoms slow down the heat transfer and thus the temperature of the dislocation core increases linearly with time. The presented results are in agreement with known experimental facts and demonstrate the importance of the heat transfer problem in the discussion of EPE.

The low-energy physics of quantum spin ice is known to support an emergent form of quantum electrodynamics (QED), where magnetic monopoles exist and the fine-structure constant is material dependent. In this article, we show how this QED is modified via a coupling to dynamical matter on the centered pyrochlore lattice, a structure that has recently been synthesized using metal-organic frameworks. Specifically, we study the low-energy properties of the $S=1/2$ quantum XXZ model on the centered pyrochlore lattice, with a focus on the sign-problem-free region. At fourth order in degenerate perturbation theory, this model hosts a quantum spin liquid distinct from the well-known U(1) quantum spin ice on the pyrochlore because of the presence of dynamical matter in the ground state. Exact diagonalization results are consistent with this quantum spin liquid over an extended region of the ground-state phase diagram, although potential quantum critical points within this region could indicate a richer phase structure. Our work thus expands the physics of quantum spin ice in an experimentally motivated geometry, showing how the emergent QED can be coupled to dynamical matter at zero temperature.

The triple perovskite oxide ${\mathrm{Ba}}_3{\mathrm{MnTa}}_2{\mathrm{O}}_9$ has been synthesized, and its magnetic properties have been investigated through dc and ac magnetization, specific heat, electron spin resonance measurements, and density functional theory (DFT) calculations. ${\mathrm{Mn}}^{2+}$ $(S=\frac{5}{2})$ ions are the only magnetic species present in the material. These ${\mathrm{Mn}}^{2+}$ ions constitute a quasi-two-dimensional triangular network in the crystallographic $ab$ plane. Magnetization and specific heat measurements reveal the absence of any long-range magnetic order down to 0.5 K despite the presence of antiferromagnetic correlations between the magnetic ions, suggesting the presence of geometric frustration in the material. The entropy release is lower than the expected theoretical value of $Rln\left(6\right)$, further suggesting the presence of frustration. First-principles calculations using DFT and atomistic spin dynamics simulations further support this lack of static magnetic order even at low temperatures and identify the competing magnetic interactions along with the quasi-two-dimensional magnetic dimensionality as the underlying origin of this unconventional magnetic behavior.

The thermoelectric effect (TE) and anomalous Nernst effect (ANE) in two-dimensional magnetic materials offer promising paths for sustainable energy generation and for overcoming technological challenges in TE devices. The advantage of ANE over the conventional Seebeck effect is the separation of electrical and thermal transport with more scalability and flexibility than conventional TE generators. This work examines the conventional TE, spin Seebeck effect (SSE), and ANE in a Janus CrTeI monolayer. We observe a large spin Seebeck coefficient for the monolayer near the Fermi level in valence- ($\sim 955 \mu {\mathrm{VK}}^{-1}$) and conduction-band ($\sim 1072 \mu {\mathrm{VK}}^{-1}$) regions at 300 K, which is desirable for spin caloritronics applications. We also found a significantly high anomalous Nernst coefficient ($N$) of $\sim 26.63 \mu {\mathrm{VK}}^{-1}$. Overall, the comprehensive investigation of conventional TE effects, SSE, and ANE in the monolayer materials reveals promising characteristics for spin caloritronics applications, high power factor ($\sim 380 \mu {\mathrm{Wm}}^{-1}{\mathrm{K}}^{-2}$), and significant Nernst coefficient. Therefore, two-dimensional CrTeI could serve as a potential platform for power generation from waste heat in quantum devices and nanoelectronics.