Condensed Matter

We study Floquet topological transition in irradiated graphene when the polarization of incident light changes randomly with time. We numerically confirm that the noise averaged time evolution operator approaches a steady value in the limit of exact Trotter decomposition of the whole period where incident light has different polarization at each interval of the decomposition. This steady limit is found to coincide with time-evolution operator calculated from the noise-averaged Hamiltonian. We observe that at the six corners (Dirac( K ) point) of the hexagonal Brillouin zone of graphene random Gaussian noise strongly modifies the phaseband structure induced by circularly polarized light whereas in zone-center ( Γ point) even a strong noise isn't able to do the same. This can be understood by analyzing the deterministic noise averaged Hamiltonian which has a different Fourier structure as well as lesser no of symmetries compared to the noise-free one. In 1D systems noise is found to renormalize the drive amplitude only.

We investigate an oblique spacetime crystal realized by a monoatomic crystal in which a mode of sound propagates. We provide a systematic analysis of the crystal and obtain the corresponding band structure, based on which the electron dynamics under an external electric field is studied. Several unique band topologies are revealed, which lead to novel Floquet-Bloch oscillations in the electron's motion. We also discover intraband Zener tunneling in the oblique spacetime crystal beyond the adiabatic limit, which effectively converts between the different band topologies. Our results indicate the possibility of a prototypical quantum acoustoelectric generator that converts energy between the sound wave and a DC electric field in quantized units.

By using the Floquet eigenstates, we derive a formula to calculate the high-harmonic components of the electric current (HHC) in the setup where a monochromatic laser field is turned on at some time. On the basis of this formulation, we study the HHC spectrum of electrons on a one-dimensional chain with the staggered potential to study the effect of multiple sites in the unit cell such as the systems with charge density wave (CDW) order. With the help of the solution for the Floquet eigenstates, we analytically show that two plateaus of different origins emerge in the HHC spectrum. The widths of these plateaus are both proportional to the field amplitude, but inversely proportional to the laser frequency and its square, respectively. We also show numerically that multi-step plateaus appear when both the field amplitude and the staggered potential are strong.

Water, in its three phases, is ubiquitous, and the surface properties of ice is important to clarifying the process of melting, as well as to various other fields, including geophysics. As such, the subject has been studied both theoretically and experimentally, for over a hundred years, while being an active field of research today. It has been established that surface melting, or premelting, exists below the melting point, and a `liquid-like layer' (LLL) exists on the surface of ice. Here, we use the surface thermal fluctuation spectra to study the properties of LLL, including its thickness, for pure ice, and for ice with impurities. We find that the properties of LLL are consistent with those of bulk liquid water, and for layers thicker than 10\,nm, their properties are experimentally indistinguishable from those of liquid water. Measured thicknesses are found to be much smaller than the previous experimental measurements close to the bulk melting temperature. We find that the additions of impurities at ppm levels cause LLL to be thicker, as well to be quite inhomogeneous, with properties depending on the dopant. This is revealed by scanning the surface at μ m level resolution, and can contribute to the slipperiness of ice in natural settings.

A quantum Monte Carlo approach, considering all the corrugation effects, was used to calculate the complete phase diagram of the second 3 He layer adsorbed on graphite. We found that a first-layer triangular solid was in equilibrium with a gas in the second layer. At a surface density 0.166±0.001 Å −2 , this fluid changes into two first-layer registered phases: 4/7 and 7/12 solids. The 7/12 arrangement transforms into an incommensurate triangular structure of ρ=0.189±0.001 Å −2 upon further helium loading. A recently proposed hexatic phase was found to be unstable with respect to those commensurate solids.

We analyse the Lifshitz pressure between silica and tin separated by a liquid mixture of bromobenzene and chlorobenzene. We show that the phase transition from semimetallic α -Sn to metallic β -Sn can switch Lifshitz forces from repulsive to attractive. This effect is caused by the difference in dielectric functions of α -Sn and β -Sn, giving both attractive and repulsive contributions to the total Lifshitz pressure at different frequency regions controlled by the composition of the intervening liquid mixture. In this way, one may be able to produce phase transition-controlled quantum levitation in liquid medium.

The heat capacity of a small amount of 3 He atoms dissolved in submonolayer 4 He film has been measured. The measured heat capacity is finite and suggests that 3 He atoms are mobile at an areal density regime higher than that of the 3 – √ × 3 – √ phase, where 4 He films are believed to be solid. Moreover, at higher areal densities, the measured heat capacity is proportional to T 2 and depends on the amounts of 3 He atoms. These behaviors are anomalous to that of a 2D Fermi fluid, and cannot be explained by uniform melting. One possible explanation for these anomalous behaviors is that helium atoms exhibit fluidity inside the domain walls of the adsorption structure, and the dissolved 3 He atoms behave as a one-dimensional Fermi fluid or as Dirac fermions, depending on the structure of the domain walls. The behaviors of the measured heat capacity strongly suggest this possibility.

We calculate the fluorescence spectra of a driven lattice of coupled cavities. To do this, we extend methods of evaluating two-time correlations in infinite lattices to open quantum systems; this allows access to momentum resolved fluorescence spectrum. We illustrate this for a driven-dissipative transverse field anisotropic XY model. By studying the fluctuation dissipation theorem, we find the emergence of a quasi-thermalized steady state with a temperature dependent on system parameters; for blue detuned driving, we show this effective temperature is negative. In the low excitation density limit, we compare these numerical results to analytical spin-wave theory, providing an understanding of the form of the distribution function and the origin of quasi-thermalization.

We found from experimental data that for noble gases and H 2 , the energy is positive for the gas phase, and negative for the liquid, possibly except the small vicinity of the critical point, about (1−T/ T c )≤0.005 . The line E= E c , in the supercritical region is found to lie close to the Widom line, where E c is the critical energy.

Formation of topological defects during symmetry breaking phase transitions via the {\it Kibble mechanism} is extensively used in systems ranging from condensed matter physics to the early stages of the universe. Kibble mechanism uses topological arguments and predicts equal probabilities for the formation of defects and anti-defects. Certain situations, however, require a net bias in the production of defects (or antidefects) during the transition, for example, superfluid transition in a rotating vessel, or flux tubes formation in a superconducting transition in the presence of external magnetic field. In this paper we present a modified Kibble mechanism for a specific system, 4 He superfluid transition in a rotating vessel, which can produce the required bias of vortices over antivortices. Our results make distinctive predictions which can be tested in superfluid 4 He experiments. These results also have important implications for superfluid phase transitions in rotating neutron stars and also for any superfluid phases of QCD arising in the non-central low energy heavy-ion collision experiment due to an overall rotation.