We consider the general problem of quenching an interacting Bose gas from the noninteracting regime to the strongly repulsive limit described by the Tonks-Girardeau gas with the initial state being a Gaussian ensemble in terms of the bosons. A generic multipoint correlation function in the steady state can be described fully in terms of a Fredholm-like determinant suitable both for a numerical and for an analytical study in certain limiting cases. Finally, we extend the study to the presence of a smooth confining potential showing that, in the thermodynamic limit, the time evolution of the two-point function can be mapped to a classical problem.

Enhanced polarization is reported in ferroelectric $(\mathrm{P}{\mathrm{b}}_{1-x}\mathrm{L}{\mathrm{a}}_x)\left(\mathrm{Z}{\mathrm{r}}_{0.52}\mathrm{T}{\mathrm{i}}_{0.48}\right){\mathrm{O}}_3$ (PLZT) thin films at low La doping concentrations. Epitaxial PLZT thin films with varying La concentrations were grown in both (001) and (111) crystallographic orientations using the conducting perovskite oxide $\mathrm{L}{\mathrm{a}}_{0.7}\mathrm{S}{\mathrm{r}}_{0.3}\mathrm{Mn}{\mathrm{O}}_3$ as the top and bottom electrodes on $\mathrm{SrTi}{\mathrm{O}}_3$ substrates by pulsed laser deposition. Dilute doping of La (0.1–0.5 at. %) was found to enhance the remanent polarizations in the PLZT films irrespective of their orientations. An increase in the remanent polarization by a factor of two is observed in the 0.5 at. % La doped PLZT thin film as compared to the undoped (Pb)$(\mathrm{Z}{\mathrm{r}}_{0.52}\mathrm{T}{\mathrm{i}}_{0.48}){\mathrm{O}}_3$ (PZT) film. The increase in polarization in the PLZT thin films was associated with the tetragonal distortion of the PLZT lattice due to the substitutional doping of La at the Pb sites, as evidenced from x-ray and microstructural analyses. Using the structural and polarization data, a linear correlation between the square of the remanent polarization and crystal-lattice distortion is obtained in the PLZT system, which corroborates with the Landau-Ginsburg-Devonshire thermodynamic model of lattice distortion-induced change in spontaneous polarization. This paper provides a novel route to enhance polarization in PLZT films, which is crucial for the coherent design of high-performance PZT-based ferroelectric and piezoelectric devices.

We demonstrate that the strain of an epitaxially grown film, which is induced by the lattice mismatch between the crystalline substrate and film and relaxes with increasing film thickness, can be conserved beyond the critical thickness of plastic relaxation of the respective film/substrate heterostructure system by adding epitaxially embedded nanoprecipitates and/or nanopillars of a secondary phase. By doing so we modify the ferroelectric properties of the film in a very controlled way. For this purpose, strained $\mathrm{N}{\mathrm{a}}_{1+x}\mathrm{Nb}{\mathrm{O}}_{3+\delta }$ films are epitaxially grown on $\left(110\right)\mathrm{NdGa}{\mathrm{O}}_3$ and their structural and electronic properties are investigated. X-ray diffraction and transmission electron microscopy analysis indicate that in addition to the epitaxially grown majority phase $\mathrm{NaNb}{\mathrm{O}}_3$, a second phase $\mathrm{N}{\mathrm{a}}_y\mathrm{Nb}{\mathrm{O}}_{3+\delta }$ is present in the films and forms crystalline precipitates and vertically aligned pillars a few nanometers in diameter. For large enough concentrations, this secondary phase appears to be able to suppress the plastic relaxation of the $\mathrm{NaNb}{\mathrm{O}}_3$ matrix. In contrast to stoichiometric films and films with small Na excess, which demonstrate strain relaxation for film thickness exceeding a few nanometers and relaxor-type ferroelectric behavior, the $\mathrm{N}{\mathrm{a}}_{1+x}\mathrm{Nb}{\mathrm{O}}_{3+\delta }$ film with the largest off-stoichiometry (grown from a target with $x=17\%$) exhibits the “classic” ferroelectric behavior of unstrained $\mathrm{NaNb}{\mathrm{O}}_3$ with a hysteretic structural and ferroelectric transition. However, the temperature of this hysteretic transition is shifted from 616 K to 655 K for unstrained material to room temperature for the strained $\mathrm{N}{\mathrm{a}}_{1+x}\mathrm{Nb}{\mathrm{O}}_{3+\delta }$ film grown from the off-stoichiometric target.

The lattice model of the Coulomb glass in two dimensions with box-type random field distribution is studied at zero temperature for system size up to ${96}^2$. To obtain the minimum energy state we annealed the system using Monte Carlo simulation followed by further minimization using cluster flipping. The values of the critical exponents are determined using the standard finite size scaling. We found that the correlation length $\xi$ diverges with an exponent $\nu =1.0$ at the critical disorder $W_c=0.2253$ and that ${\chi }_{\mathrm{dis}}\approx {\xi }^{4-\overline{\eta }}$ with $\overline{\eta }=2$ for the disconnected susceptibility. The staggered magnetization behaves discontinuously around the transition and the critical exponent of magnetization $\beta =0$. The probability distribution of the staggered magnetization shows a three peak structure which is a characteristic feature for the phase coexistence at first-order phase transition. In addition to this, at the critical disorder we have also studied the properties of the domain for different system sizes. In contradiction with the Imry-Ma arguments, we found pinned and noncompact domains where most of the random field energy was contained in the domain wall. Our results are also inconsistent with Binder's roughening picture.

Magnetic, electronic, and structural properties of $M\mathrm{F}{\mathrm{e}}_2{\mathrm{O}}_4 (M=\mathrm{Mg},\mathrm{Zn},\mathrm{Fe})$ ferric spinels have been studied by ${}^{57}\mathrm{Fe}$ Mössbauer spectroscopy, electrical conductivity, and powder and single-crystal x-ray diffraction (XRD) to a pressure of 120 GPa and in the 2.4–300 K temperature range. These studies reveal for all materials, at the pressure range 25–40 GPa, an irreversible first-order structural transition to the postspinel $\mathrm{CaT}{\mathrm{i}}_2{\mathrm{O}}_4-$ type structure (Bbmm) in which the HS $\mathrm{F}{\mathrm{e}}^{3+}$ occupies two different crystallographic sites characterized by six- and eightfold coordination polyhedra, respectively. Above 40 GPa, an onset of a sluggish second-order high-to-low spin (HS-LS) transition is observed on the octahedral $\mathrm{F}{\mathrm{e}}^{3+}$ sites while $\mathrm{F}{\mathrm{e}}^{3+}$ occupying bicapped trigonal prism sites remain in the HS state. Despite an appreciable resistance decrease, corroborating with the transition to the LS state, $\mathrm{MgF}{\mathrm{e}}_2{\mathrm{O}}_4$ and $\mathrm{ZnF}{\mathrm{e}}_2{\mathrm{O}}_4$ remain semiconductors at this pressure range. However, in the case of $\mathrm{F}{\mathrm{e}}_3{\mathrm{O}}_4$, the second-order HS-LS transition on the $\mathrm{F}{\mathrm{e}}^{3+}$ octahedral sites corroborates with a clear trend to a gap closure and formation of a semimetal state above 50 GPa. Above 65 GPa, another structural phase transition is observed in $\mathrm{F}{\mathrm{e}}_3{\mathrm{O}}_4$ to a new Pmma structure. This transition coincides with the onset of nonmagnetic $\mathrm{F}{\mathrm{e}}^{2+}$, signifying further propagation of the gradual collapse of magnetism corroborating with a sluggish metallization process. With this, half of $\mathrm{F}{\mathrm{e}}^{3+}$ sites remain in the HS state. Thus, this paper demonstrates that, in a material with a complex crystal structure containing transition metal cation(s) in different environments, a HS-LS transition and delocalization/metallization of the $3d$ electrons does not necessarily occur simultaneously and may propagate through different crystallographic sites at different degrees of compression.

The electronic transport properties of the Si(111)-$(\sqrt{3}\times \sqrt{3})$-Sn surface formed on the low-doped Si substrates are studied using two-probe conductivity measurements and tunneling spectroscopy. We demonstrate that the ground state corresponds to a Mott-Hubbard insulator with a band gap of $2\mathrm{\Delta }\approx 70\mathrm{meV}$, which vanishes quickly upon the temperature increase at $T\sim 30–40\mathrm{K}$. The energy gap at the Fermi level observed in tunneling spectroscopy measurements at higher temperatures could be described in terms of the dynamic Coulomb blockade approximation. The temperature dependence of the surface conductivity above 45 K corresponds to the Efros-Shklovskii hopping conduction law. The obtained localization length of the electron is $\xi \approx 7\AA$.

The multiscale entanglement renormalization ansatz (MERA) is a tensor network based variational ansatz that is capable of capturing many of the key physical properties of strongly correlated ground states such as criticality and topological order. MERA also shares many deep relationships with the AdS/CFT (gauge-gravity) correspondence by realizing a UV complete holographic duality within the tensor networks framework. Motivated by this, we have repurposed the MERA tensor network as an analysis tool to study the real-time evolution of the 1D transverse Ising model in its low-energy excited state sector. We performed this analysis by allowing the ancilla qubits of the MERA tensor network to acquire quantum fluctuations, which yields a unitary transform between the physical (boundary) and ancilla qubit (bulk) Hilbert spaces. This then defines a reversible quantum circuit, which is used as a “holographic transform” to study excited states and their real-time dynamics from the point of the bulk ancillae. In the gapped paramagnetic phase of the transverse field Ising model, we demonstrate the holographic duality between excited states induced by single spin-flips (Ising “magnons”) acting on the ground state and single ancilla qubit spin flips. The single ancillae qubit excitation is shown to be stable in the bulk under real-time evolution and hence defines a stable holographic quasiparticle, which we have named the “hologron.” Their bulk 2D Hamiltonian, energy spectrum, and dynamics within the MERA network are studied numerically. The “dictionary” between the bulk and boundary is determined and realizes many features of the holographic correspondence in a non-CFT limit of the boundary theory. As an added spin-off, this dictionary together with the extension to multihologron sectors gives us a systematic way to construct quantitatively accurate low-energy effective Hamiltonians.

The electron spin dynamics in an optically excited narrow quantum well is studied, where the electron spins precess in a $\mathbf{k}$-dependent magnetic field, while the electrons scatter at localized impurities. For the resulting spin decay, which is commonly known as the D'yakonov-Perel' mechansim, analytical expressions in the strong- and weak-scattering limits are available. It is found by the numerical solution of quantum kinetic equations in a broad range of parameters that, in situations that are typically relevant for ultrafast optical experiments, the dynamics of the total spin polarization significantly deviates from the pertinent analytical results. This is attributed to the broad spectral width of the optically excited spin-polarized electron distribution, which gives rise to a spin dephasing due to inhomogeneous broadening. Furthermore, it is found that the decay of the spin polarization need not be exponential. The notion of a spin decay time becomes ambiguous and different definitions of spin decay times can lead to different outcomes. The long-term dynamics of the decay of the spin polarization is even dominated by an algebraically decaying component. These findings highlight the importance of the effects of the broad spectral distribution of optically excited carriers in ultrashort magneto-optical experiments.

We study the bound and antibound states of two excitons in a GaAs single quantum well by two-dimensional coherent spectroscopy. We also propose a method to directly observe the amplitude and phase (real and imaginary parts) of optical fields by using a heterodyne interference technique and through synchronized detection of the interference signals. In this scheme, the mechanical fluctuation of an unstabilized interferometer does not affect the measurement. In addition, the amplitude and phase of the optical fields, resulting from the coherent interactions between light and matter, are directly obtained by comparing a reference heterodyne beating signal by using a two-phase lock-in amplifier. By using this method, the bound and antibound states of two excitons are observed. It is expected that the excitons are localized to the quantum islands and the lateral confinement induces the large repulsive energy between the two excitons.

We perform precise measurements of the permanent dipole moment and polarizability of both the neutral exciton ($X^0$) and positive trion ($X^{+}$) in a single InAs/GaAs self-assembled quantum dot (QD). This is achieved through one- and two-color high-resolution photocurrent (PC) spectroscopy of $X^0$ and $X^{+}$, respectively, using ultra-narrow-bandwidth continuous-wave lasers. This technique allows for sub-μeV resolution, which is limited only by the spectral linewidth of the lasers and is more than four orders of magnitude higher than that of previous techniques. We are therefore permitted to obtain precise values for the permanent dipole moment and polarizability of both $X^0$ and $X^{+}$, by fitting an appropriate theoretical model to the measured transition energies as a function of electric field. As a sequence of protocols for the optical initialization, manipulation, and readout of a QD hole spin qubit embedded in a photodiode device relies on the coherent control of both $X^0$ and $X^{+}$ as intermediary states, such precise measurements of their dipole moment and polarizability using high-resolution PC spectroscopy are crucial for implementing these quantum computing protocols with high fidelity.

Single photons from semiconductor quantum dots are promising resources for linear optical quantum computing, or, when coupled to spin states, quantum repeaters. To realize such schemes, the photons must exhibit a high degree of indistinguishability. However, the solid-state environment presents inherent obstacles for this requirement as intrinsic semiconductor fluctuations can destroy the photon indistinguishability. Here, we demonstrate that resonant excitation of a quantum dot with a narrow-band laser generates near transform limited power spectra and indistinguishable photons from a single quantum dot in an environment with many charge-fluctuating traps. The specificity of the resonant excitation suppresses the excited state population in the quantum dot when it is detuned due to spectral fluctuations. The dynamics of this process lead to flickering of the emission over long time scales ($>5\mu \text{s}$) and reduces the time-averaged count rates. Nevertheless, in spite of significant spectral fluctuations, high visibility two-photon interference can be achieved. This approach is useful for quantum dots with nearby surface states in processed photonic structures and quantum emitters in emerging platforms, such as two-dimensional semiconductors.

Topological insulators are characterized by the quantum anomalous Hall effect (QAHE) on the topological surface states under time-reversal symmetry breaking. Motivated by recent experiments on the magneto-optical effects induced by the QAHE, we develop a theory for the dynamical Hall conductivity for subgap optical frequency and intense optical fields using the Keldysh-Floquet Green's function formalism. Our theory reveals a nonlinear regime in which the Hall conductivity remains close to $e^2/2h$ at low frequencies. At higher optical fields, we find that the subsequent collapse of the half quantization is accompanied by coherent oscillations of the dynamical Hall conductivity as a function of field strength, triggered by the formation of Floquet subbands and the concomitant intersubband transitions.

We construct a dual-bosonized description of a massless Majorana fermion in (2+1)$d$. In contrast to Dirac fermions, for which a bosonized description can be constructed using a flux attachment procedure, neutral Majorana fermions call for a different approach.We argue that the dual theory is an $\mathrm{SO}{\left(N\right)}_1$ Chern-Simons gauge theory with a critical $\mathrm{SO}\left(N\right)$ vector bosonic matter field ($N\ge 3$). The monopole of the $\mathrm{SO}\left(N\right)$ gauge field is identified with the Majorana fermion. We provide evidence for the duality by establishing the correspondence of adjacent gapped phases and by a parton construction. We also propose a generalization of the duality to $N_f$ flavors of Majorana fermions, and discuss possible resolutions of a caveat associated with an emergent global $Z_2$ symmetry. Finally, we conjecture a dual description of an $\mathcal{N}=1$ supersymmetric fixed point in (2+1)$d$, which is realized by tuning a single flavor of Majorana fermions to an interacting (Gross-Neveu) critical point.

The unconventional magnetotransport at the interface between transition-metal oxides ${\mathrm{LaAlO}}_3$ ($\mathrm{LAO}$) and ${\mathrm{SrTiO}}_3$ ($\mathrm{STO}$) is frequently related to mobile electrons interacting with localized magnetic moments. However, nature and properties of magnetism at this interface are not well understood so far. In this paper, we focus on transport effects driven by spin-orbit coupling and intentionally neglect possible strong correlations. The electrical resistivity tensor is calculated as a function of the magnitude and orientation of an external magnetic field parallel to the interface. The semiclassical Boltzmann equation is solved numerically for the two-dimensional system of spin-orbit coupled electrons accelerated by an electric field and scattered by spatially correlated impurities. At temperatures of a few Kelvin and densities such that the chemical potential crosses the second pair of spin-orbit split bands, we find a strongly anisotropic modulation of the (negative) magnetoresistance above $10\mathrm{T}$, characterized by multiple maxima and minima away from the crystalline axes. Along with the drop of the magnetoresistance, an abrupt enhancement of the transverse resistivity occurs. The angular modulation of the latter considerably deviates from a (low-field) sinusoidal dependence to a (high-field) step-like behavior. These peculiar features are the consequences of the anisotropy of both intraband and interband scattering amplitudes in the Brillouin zone when the relevant energy scales in the system—chemical potential, spin-orbit interaction, and Zeeman energy—are all comparable to each other. The theory provides good qualitative agreement with experimental data in the literature.

Low-energy excitations in graphene exhibit relativistic properties due to the linear dispersion relation close to the Dirac points in the first Brillouin zone. Two of the Dirac points located at opposite corners of the first Brillouin zone can be chosen as inequivalent, representing a new valley degree of freedom, in addition to the charge and spin of an electron. Using the valley degree of freedom to encode information has attracted significant interest, both theoretically and experimentally, and gave rise to the field of valleytronics. We study a graphene $p-n$ junction in a uniform out-of-plane magnetic field as a platform to generate and controllably manipulate the valley polarization of electrons. We show that by tuning the external potential giving rise to the $p-n$ junction we can switch the current from one valley polarization to the other. We also consider the effect of different types of edge terminations and present a setup where we can partition an incoming valley-unpolarized current into two branches of valley-polarized currents. The branching ratio can be chosen by changing the location of the $p-n$ junction using a gate.

Detailed investigation of ${\mathrm{Ca}}_2{\mathrm{CoSi}}_2{\mathrm{O}}_7$ was performed in its low-temperature magnetoelectric state combining neutron diffraction with magnetization measurements on single crystals. The crystal and magnetic structures well below the antiferromagnetic transition temperature of $T_{\text{N}}\approx 5.7$ K were determined using neutron diffraction. Neutron diffraction data imply no structural phase transition from 10 K down to 2.5 K and are well described within the orthorhombic space group $P{2}_1{2}_{1}2$ with a $3\times 3\times 1$ supercell compared with the high-temperature unmodulated state (tetragonal space group $P\overline{4}{2}_{1}m$). We found that in zero magnetic field the magnetic space group is $P{2}_1{2}_1^{\prime }{2}^{\prime }$ with antiferromagnetic order along the [100] or [010] axes for two types of ${90}^{\circ }$ twin domains, while neighboring spins along the [001] axis are ordered ferromagnetically. A noncollinear spin arrangement due to small canting within the $ab$ plane is allowed by symmetry and leads to the existence of the tiny spontaneous magnetization below $T_{\text{N}}$. The ordered moment with a magnitude of about 2.8 ${\mu }_{\text{B}}/{\mathrm{Co}}^{2+}$ at 2.5 K lies in the $ab$ plane. Distinct differences between the magnetic structure of ${\mathrm{Ca}}_2{\mathrm{CoSi}}_2{\mathrm{O}}_7$ as compared to those of ${\mathrm{Ba}}_2{\mathrm{CoGe}}_2{\mathrm{O}}_7$ and ${\mathrm{Sr}}_2{\mathrm{CoSi}}_2{\mathrm{O}}_7$ are discussed.

Thermal lattice expansion of the Invar ${\mathrm{Fe}}_{0.65}{\mathrm{Ni}}_{0.35}$ alloy is investigated in first-principles calculations using the spin-wave method, which is generalized here for the ferromagnetic state with short-range order. It is shown that magnetic short-range order effects make a substantial contribution to the equilibrium lattice constant and cannot be neglected in the accurate ab initio modeling of the thermal expansion in Fe-Ni alloys. We also demonstrate that at high temperatures, close to and above the magnetic transition, magnetic entropy associated with transverse and longitudinal spin fluctuations yields a noticeable contribution to the equilibrium lattice constant. The obtained theoretical results for the temperature dependent lattice constant are in semiquantitative agreement with the experimental data apart from the region close the magnetic transition.

We report on the crystal and magnetic structures, magnetic, transport, and thermal properties of ${\mathrm{U}}_2{\mathrm{Rh}}_2\mathrm{Sn}$ single crystals studied in part in high magnetic fields up to 58 T. The material adopts a ${\mathrm{U}}_3{\mathrm{Si}}_2$-related tetragonal crystal structure and orders antiferromagnetically below $T_N=25$ K. The antiferromagnetic structure is characterized by a propagation vector $\mathit{k}=\left(00\frac{1}{2}\right)$. The magnetism in ${\mathrm{U}}_2{\mathrm{Rh}}_2\mathrm{Sn}$ is found to be associated mainly with $5f$ states. However, both unpolarized and polarized neutron experiments reveal at low temperatures in zero field non-negligible magnetic moments also on Rh sites. U moments of 0.50(2) ${\mu }_B$ are directed along the tetragonal axis while Rh moments of 0.06(4) ${\mu }_B$ form a noncollinear arrangement confined to the basal plane. The response to applied magnetic field is highly anisotropic. Above $\sim 15\mathrm{K}$ the easy magnetization direction is along the tetragonal axis. At lower temperatures, however, a stronger response is found perpendicular to the $c$ axis. While for the $a$ axis no magnetic phase transition is observed up to 58 T, for the field applied at 1.8 K along the tetragonal axis we observe above 22.5 T a field-polarized state. A magnetic phase diagram for the field applied along the $c$ axis is presented.

Single-crystal x-ray diffraction in pulsed magnetic fields of up to 31 T was used to investigate the iron telluride antiferromagnet ${\mathrm{Fe}}_{1.1}\mathrm{Te}$, which is a parent of the Fe-based chalcogenide superconductors. At temperatures below the Néel temperature $T_N\simeq 60$ K, high magnetic fields perpendicular to the $c$ axis lead to an irreversible detwinning of the crystal at the field $H_R$, where magnetocrystalline domains are selected by a moment reorientation process. Just below $T_N$, the onset of a structural transition at the critical field $H_C>H_R$, which delimits the antiferromagnet phase, indicates a partial restoration of the high-temperature tetragonal symmetry. The lattice and magnetic answers to an in-plane magnetic field are discussed, emphasizing the strength of magnetoelastic coupling in ${\mathrm{Fe}}_{1.1}\mathrm{Te}$.