#### Physical Review B

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ISSN / EISSN : 2469-9950 / 2469-9969
Total articles ≅ 29,308
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#### Latest articles in this journal

, Daisuke Miura, Akimasa Sakuma, Jakub Železný
Published: 14 September 2021
Physical Review B, Volume 104; https://doi.org/10.1103/physrevb.104.094417

Abstract:
The spin Hall effect (SHE) is responsible for electrical spin current generation, which is a key concept of modern spintronics. We present a theoretical study of an extrinsic mechanism of SHE arising from a spin-dependent s-d scattering in ferromagnets. In order to investigate the spin conductivity in a ferromagnetic $3d$ alloy model, we employ a microscopic transport theory based on the Kubo formula and the averaged $T$-matrix approximation. From the model, we derived an extrinsic mechanism that contributes to both the SHE and the time-reversal odd SHE known as the magnetic SHE. This mechanism can be understood as the contribution from anisotropic (spatial-dependent) spin-flip scattering due to the combination of the orbital-dependent anisotropic shape of s-d hybridization and spin flipping, with the orbital shift caused by spin-orbit interaction with the $d$ orbitals. We also show that this mechanism is valid under crystal-field splitting among the $d$ orbitals in either the cubic or tetragonal symmetry.
Akihiro Koide, Takuji Nomura,
Published: 14 September 2021
Physical Review B, Volume 104; https://doi.org/10.1103/physrevb.104.094419

Abstract:
We propose sum rules of x-ray magnetic circularly polarized emission (XMCPE) at $L$ edges for $3d$ transition metals. By making use of combinations of incident and emitted photon helicities, $z$-component expectation values of spin, orbital, magnetic dipole, and quadrupole terms can be obtained separately. The fundamental difference in the sum rules between x-ray magnetic circular dichroism and XMCPE arises from the variety of electron transitions involving core states split by the spin-orbit interaction. The additional electron transition in XMCPE causes complicated angular dependence of the sum rule relation for the spin moment. Our findings promote future $L$-edge XMCPE measurements, which have not been observed at present.
Javier Lopez-Piqueres, Brayden Ware, Sarang Gopalakrishnan, Romain Vasseur
Published: 14 September 2021
Physical Review B, Volume 104; https://doi.org/10.1103/physrevb.104.104307

Abstract:
Operator spreading under unitary time evolution has attracted a lot of attention recently as a way to probe many-body quantum chaos. While quantities such as out-of-time-ordered correlators (OTOCs) do distinguish interacting from noninteracting systems, it has remained unclear to what extent they can truly diagnose chaotic vs integrable dynamics in many-body quantum systems. Here, we analyze operator spreading in generic one-dimensional many-body quantum systems using a combination of matrix product operator (MPO) and analytical techniques, focusing on the operator right weight. First, we show that while small bond dimension MPOs allow one to capture the exponentially decaying tail of the operator front, in agreement with earlier results, they lead to significant quantitative and qualitative errors for the actual front—defined by the maximum of the right weight. We find that while the operator front broadens diffusively in both integrable and chaotic interacting spin chains, the precise shape and scaling of the height of the front in integrable systems is anomalous for all accessible times. We interpret these results using a quasiparticle picture. This provides a sharp, although rather subtle, signature of many-body quantum chaos in the operator front.
Laura Classen,
Published: 14 September 2021
Physical Review B, Volume 104; https://doi.org/10.1103/physrevb.104.125120

Abstract:
We study a model of $N$ fermions in a quantum dot, coupled to $M$ bosons by a disorder-induced complex Yukawa coupling [Yukawa Sachdev-Ye-Kitaev (SYK) model], in order to explore the interplay between non-Fermi liquid and superconductivity in a strongly coupled, (quantum-)critical environment. We analyze the phase diagram of the model for an arbitrary complex interaction and arbitrary ratio of $N/M$, with special focus on the two regimes of non-Fermi-liquid behavior: an SYK-like behavior with a power-law frequency dependence of the fermionic self-energy and an impuritylike behavior with frequency independent self-energy. We show that the crossover between the two can be reached by varying either the strength of the fermion-boson coupling or the ratio $M/N$. We next argue that in both regimes the system is unstable to superconductivity if the strength of time-reversal-symmetry-breaking disorder is below a certain threshold. We show how the corresponding onset temperatures vary between the two regimes. We argue that the superconducting state is highly unconventional with an infinite set of minima of the condensation energy at $T=0$, corresponding to topologically different gap functions. We discuss in detail similarities and differences between this model and the model of dispersion-full fermions tuned to a metallic quantum-critical point, with an effective singular dynamical interaction $V\left(\mathrm{\Omega }\right)\propto 1/{|\mathrm{\Omega }|}^{\gamma }$ (the $\gamma$ model).
R. S. Malik, E. K. Delczeg-Czirjak, R. Knut, D. Thonig, I. Vaskivskyi, D. Phuyal, , S. Jana, R. Stefanuik, Y. O. Kvashnin, et al.
Published: 14 September 2021
Physical Review B, Volume 104; https://doi.org/10.1103/physrevb.104.l100408

Abstract:
We report on optically induced, ultrafast magnetization dynamics in the Heusler alloy ${\mathrm{Co}}_{2}\mathrm{FeAl}$, probed by time-resolved magneto-optical Kerr effect. Experimental results are compared to results from electronic structure theory and atomistic spin-dynamics simulations. Experimentally, we find that the demagnetization time (${\tau }_{M}$) in films of ${\mathrm{Co}}_{2}\mathrm{FeAl}$ is almost independent of varying structural order, and that it is similar to that in elemental 3$d$ ferromagnets. In contrast, the slower process of magnetization recovery, specified by ${\tau }_{R}$, is found to occur on picosecond time scales, and is demonstrated to correlate strongly with the Gilbert damping parameter ($\alpha$). Based on these results we argue that for ${\mathrm{Co}}_{2}\mathrm{FeAl}$ the remagnetization process is dominated by magnon dynamics, something which might have general applicability.
, Xiao Chen, , Matthew P. A. Fisher
Published: 14 September 2021
Physical Review B, Volume 104; https://doi.org/10.1103/physrevb.104.104305

Abstract:
We establish the emergence of a conformal field theory (CFT) in a (1+1)-dimensional hybrid quantum circuit right at the measurement-driven entanglement transition by revealing space-time conformal covariance of entanglement entropies and mutual information for various subregions at different circuit depths. While the evolution takes place in real time, the spacetime manifold of the circuit appears to host a Euclidean field theory with imaginary time. Throughout the paper we investigate Clifford circuits with several different boundary conditions by injecting physical qubits at the spatial and/or temporal boundaries, all giving consistent characterizations of the underlying “Clifford CFT.” We emphasize (super)universal results that are consequences solely of the conformal invariance and do not depend crucially on the precise nature of the CFT. Among these are the infinite entangling speed as a consequence of measurement-induced quantum nonlocality and the critical purification dynamics of a mixed initial state.
F. Giusti, A. Montanaro, , , , F. Glerean, G. Jarc, H. Eisaki, M. Greven, A. Damascelli, et al.
Published: 14 September 2021
Physical Review B, Volume 104; https://doi.org/10.1103/physrevb.104.125121

Abstract:
Superconductivity in the cuprates is characterized by an anisotropic electronic gap of $d$-wave symmetry. The aim of this work is to understand how this anisotropy affects the nonequilibrium electronic response of high-${T}_{c}$ superconductors. Here we use a polarization selective time domain experiment to address the dynamics of electronic excitation of different symmetry in optimally doped ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{Y}}_{0.08}{\mathrm{Ca}}_{0.92}{\mathrm{Cu}}_{2}{\mathrm{O}}_{8+\delta }$ and measure the nodal and antinodal nonequilibrium response resulting from photoexcitations with ultrashort pulses with photon energy comparable to the superconducting gap. The response to long wavelength photoexcitation with pump polarization along the Cu-Cu axis of the sample is discussed with the support of an effective $d$-wave BCS model which suggests that such transient response could be ascribed to an increase of pair coherence in the antinodal region.
Vinitha Balachandran, , Giulio Casati, Dario Poletti
Published: 14 September 2021
Physical Review B, Volume 104; https://doi.org/10.1103/physrevb.104.104306

Abstract:
The relaxation of out-of-time-ordered correlators (OTOCs) has been studied as a means to characterize the scrambling properties of a quantum system. We show that the presence of local conserved quantities typically results in, at the fastest, an algebraic relaxation of the OTOC provided (i) the dynamics is local and (ii) the system follows the eigenstate thermalization hypothesis. Our result relies on the algebraic scaling of the infinite-time value of OTOCs with system size, which is typical in thermalizing systems with local conserved quantities, and on the existence of finite speed of propagation of correlations for finite-range-interaction systems. We show that time independence of the Hamiltonian is not necessary as the above conditions (i) and (ii) can occur in time-dependent systems, both periodic or aperiodic. We also remark that our result can be extended to systems with power-law interactions.
W. Pfäffle, D. Antonov, J. Wrachtrup,
Published: 14 September 2021
Physical Review B, Volume 104; https://doi.org/10.1103/physrevb.104.104105

Abstract:
We present a computational approach, based on density functional theory and screened configuration interaction, able to accurately treat highly correlated electron spins localized around semiconductor defects, typically occurring in the context of qubit implementations. The method is computationally not more demanding than a usual density functional theory calculation, which makes it suitable for the calculation of isolated defects, or defect complexes, typically requiring large simulation cells. We illustrate the approach by applying it to the three different charge states of the nitrogen vacancy defect in diamond and obtain very good agreement with experiment.
Chen Lu, Meng-Meng Gao, Ting-Ting Hu,
Published: 14 September 2021
Physical Review B, Volume 104; https://doi.org/10.1103/physrevb.104.115304

Abstract:
The physical model of nanosecond laser ablation of semi-insulating 4H-SiC irradiated by KrF excimer laser with a wavelength of 248 nm was studied. The etching depth was tested by a stylus surface profiler. The morphology of the ablation pit and the thickness of the damaged layer were observed through scanning electron microscope. The phases at the laser irradiated surface were analyzed by Raman spectroscopy. In situ x-ray photoelectron spectroscopy was used to obtain component distribution of the damaged layer and a reasonable thermophysical model was constructed. The temperature distribution of the substrate after the laser irradiation was calculated according to this model. It was found that the etching depth had a linear relationship with the number of laser pulses and the thickness of the uniform damaged layer was independent of pulse number $\left(>10\right)$. The thickness of the ablated layer and the newly generated damaged layer are equivalent for each laser irradiation. The established laser ablation model deepens the understanding of physical process and mechanism of nanosecond laser etching of SiC and provides a theoretical guidance for laser processing of SiC.