Detection of BCS pairing in neutral fermi fluids via stokes scattering: the Hebel-Slichter effect

We consider the effects of superfluidity on the light scattering properties of a two component gas of fermionic atoms, demonstrating that the scattered intensities of the Stokes and anti-Stokes lines exhibit a large maximum below the critical temperature when the gas is superfluid. This effect, the light scattering analog of the Hebel-Slichter effect in conventional superconductors, can be used to detect unambiguously the onset of pairing in an atomic gas in the BCS regime.     

Spin-triplet pairing instability of the spinon fermi surface in a U(1) spin liquid

Recent experiments on the organic compound kappa-(ET)2Cu2(CN)3 have provided a promising example of a two-dimensional spin liquid state. This phase is described by a two-dimensional spinon Fermi sea coupled to a U(1) gauge field. We study Kohn-Luttinger-like pairing instabilities of the spinon Fermi surface due to singular interaction processes with twice-the-Fermi-momentum transfer. We find that under certain circumstances the pairing instability occurs in odd-orbital-angular momentum or spin-triplet channels. Implications to experiments are discussed.     

Observation of phase separation in a strongly interacting imbalanced fermi gas

We have observed phase separation between the superfluid and the normal component in a strongly interacting Fermi gas with imbalanced spin populations. The in situ distribution of the density difference between two trapped spin components is obtained using phase-contrast imaging and 3D image reconstruction. A shell structure is clearly identified where the superfluid region of equal densities is surrounded by a normal gas of unequal densities. The phase transition induces a dramatic change in the density profiles as excess fermions are expelled from the superfluid.     

Polynomial-time simulation of pairing models on a quantum computer

We propose a polynomial-time algorithm for simulation of the class of pairing Hamiltonians, e.g., the BCS Hamiltonian, on an NMR quantum computer. The algorithm adiabatically finds the low-lying spectrum in the vicinity of the gap between the ground and the first excited states and provides a test of the applicability of the BCS Hamiltonian to mesoscopic superconducting systems, such as ultrasmall metallic grains.     

Finite-temperature phase diagram of a polarized fermi gas in an optical lattice

We present phase diagrams for a polarized Fermi gas in an optical lattice as a function of temperature, polarization, and lattice filling factor. We consider the Fulde-Ferrel-Larkin-Ovchinnikov (FFLO), Sarma or breached pair, and BCS phases, and the normal state and phase separation. We show that the FFLO phase appears in a considerable portion of the phase diagram. The diagrams have two critical points of different nature. We show how various phases leave clear signatures to momentum distributions of the atoms which can be observed after time of flight expansion.     

Dynamic projection on feshbach molecules: a probe of pairing and phase fluctuations

We describe and justify a simple model for the dynamics associated with rapid sweeps across a Feshbach resonance, from the atomic to the molecular side, in an ultracold Fermi system. The model allows us to relate the observed molecule momentum distribution to equilibrium properties of the initial state. In particular, the dependence of the total molecule number on the sweep rate is found to be a sensitive probe of pairing in the initial state, whether condensed or not. This can be used to establish the presence of a phase fluctuation induced "pseudogap" phase in these systems.     

Possible polarized neutron-nucleus scattering search for a new spin-dependent nucleon-nucleon coupling in the fermi range

An experimental opportunity is presented for the future to measure possible P- and T-non-invariant axion-like interaction between nucleons in the Fermi range. This interaction may be searched for in the measurement spin-dependent asymmetry of scattering of polarized neutrons in a keV-MeV energy range by heavy nuclei.     

Model of an exotic chiral superconducting phase in a graphene bilayer

We theoretically demonstrate the formation of a new type of unconventional superconductivity in graphene materials, which exhibits a gapless property. The studied superconductivity is based on an interlayer pairing of chiral electrons in bilayer graphene, which results in an exotic s-wave spin-triplet condensate order with anomalous thermodynamic properties. These include the possibility of a temperature-induced condensation causing an increase of the pairing gap with increasing temperature and an entropy of the stable superconducting state which can be higher than its value in the normal state. Our study reveals the analogy of the interlayer superconductivity in graphene materials to the color superconductivity in dense quark matter and the gapless pairing states in nuclear matter and ultracold atomic gases.     

Light exotic nuclei: A new explanation of halo

The experimental Tanihata density distributions for both protons and neutrons in ^6,8He are very well reproduced here without an increase of the 1p neutron orbital size. Instead, an internal collective rotation, due to the invalidity of the adiabatic approximation, leads to the same measurable increase in the radius and to a simultaneous decrease in the separation energy of the nucleons participating in this rotation. Further support of the approach presented is gained by the reproduction of the ground-state properties of ^7–11Be and of the excited (particle and rotational) states of ¹¹Be.     

Mean-field pairing theory for the charge-stripe phase of high-temperature cuprate superconductors

Striped high-T(c) superconductors such as La(2-y-x)Nd(y)Sr(x)CuO(4) and La(2-x)Ba(x)CuO(4) near x = 1/8 show a fascinating competition between spin and charge order and superconductivity. A theory for these systems therefore has to capture both the spin correlations of an antiferromagnet and the pair correlations of a superconductor. For this purpose we present here an effective Hartree-Fock theory incorporating both electron pairing with finite center-of-mass momentum and antiferromagnetism. We show that this theory reproduces the key experimental features such as the formation of the antiferromagnetic stripe patterns at 7/8 band filling or the quasi-one-dimensional electronic structure observed by photoemission spectroscopy.     

Scattering phase of quantum dots: emergence of universal behavior

We investigate scattering through chaotic ballistic quantum dots in the Coulomb-blockade regime. Focusing on the scattering phase, we show that large universal sequences emerge in the short wavelength limit, where phase lapses of π systematically occur between two consecutive resonances. Our results are corroborated by numerics and are in qualitative agreement with existing experiments.     

时间晶体：一种新物态的探索

由于其迷人的魅力,晶体在过去几个世纪里一直吸引着我们的注意。人们所熟知的晶体,从雪花到钻石,通常都是由原子或分子在空间中规则排列所构成的。对晶体的研究帮助我们建立了一整套框架,可以用于理解其他的空间有序相,例如超导体、液晶和铁磁相。     

Possibility of a condensed phase of excitons because of phonon induced exciton-exciton pairing

In this paper we study the phonon-induced exciton-exciton interaction. It is found that the interaction can be attractive under certain conditions. Taking into account this attractive interaction, the pairing of excitons with opposite momenta is studied and the excitation spectrum determined. The results are similar to a system of bosons. There appears to be some possibility of superfluid behaviour.     

Quantum well of a new type based on gapless graphene with different fermi velocities

The energy spectrum of a new-type quantumwell composed of gapless graphenes with identical work functions and different Fermi velocities is investigated. Symmetric and asymmetric quantum wells are considered. In a symmetric well, there is always at least one bound state. In an asymmetric well, a bound state appears, beginning at a certain finite momentum. A possibility of appearance of boundary states is investigated.     

A new exotic state in an old material: a tale of SmB6

We review current theoretical and experimental efforts to identify a novel class of intermetallic 4f and 5f orbital materials in which strong interactions between itinerant and predominately localized degrees of freedom give rise to a bulk insulating state at low temperatures, while the surface remains metallic. This effect arises due to inversion of even-parity conduction bands and odd-parity very narrow f-electron bands. The number of band inversions is mainly determined by the crystal symmetry of a material and the corresponding degeneracy of the hybridized f-electron bands. For an odd number of band inversions, the metallic surface states are chiral and therefore remain robust against disorder and time-reversal invariant perturbations. We discuss a number of unresolved theoretical issues specific to topological Kondo insulators and outline experimental challenges in probing the chiral surface states in these materials.     

Conditions for the emergence of spatially asymmetric retrieval states in an attractor neural network

In this paper we show that during the retrieval process in a binary symmetric Hebb neural network, spatially localized states can be observed when the connectivity of the network is distance-dependent and a constraint on the activity of the network is imposed, which forces different levels of activity in the retrieval and learning states. This asymmetry in the activity during retrieval and learning is found to be a sufficient condition to observe spatially localized retrieval states. The result is confirmed analytically and by simulation.     

Generating functional models for a statistical system near a phase transition

Starting from an assumed form of the distribution function near the phase transition point, an expression for the generating functional of a statistical system suitable for describing two-phase states of matter is derived. We then obtain formulas for the partition function and correlation functions by the standard procedure.     

Quantum collisional evolution of a one-dimensional fermi gas: Numerical solution

We present a numerical solution to the problem of the quantum collisional evolution of a one-dimensional Fermi gas. The equation governing this dynamics is non-markovian non-linear and can be solved exactly in this case. We observe two distinct time scales associated with the relaxation process, one connected with the establishment of correlations in the system and which is very short as compared to the second one, related to the evolution of the one-body density, once correlations are established.