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1.
Within a quantum virial expansion, we investigate theoretically the violation of universal thermodynamics for a strongly interacting unitary Fermi gas trapped in a harmonic potential. The violation is caused by the existence and anisotropy of the trapping potential and a finite-range of the two-body interaction. We calculate the second virial coefficient by solving a two-fermion problem in 3D uniform harmonic traps, as well as in anisotropic traps. In the unitarity limit, the universal value of the trapped second virial coefficient is 1/4. We discuss in detail the non-universal correction to the second virial coefficient and to the equation of state. 相似文献
2.
Fulde–Ferrell–Larkin–Ovchinnikov states in equally populated Fermi gases in a two-dimensional moving optical lattice
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《中国物理 B》2021,30(10):100305-100305
We study the possibility of stabilizing a Fulde–Ferrell–Larkin–Ovchinnikov(FFLO) state in an equally populated two-component Fermi gas trapped in a moving two-dimensional optical lattice. For a system with nearly half filling, we find that a finite pairing momentum perpendicular to the moving direction can be spontaneously induced for a proper choice of lattice velocity. As a result, the total pairing momentum is tilted towards the nesting vector to take advantage of the significant enhancement of the density of states. 相似文献
3.
Jia-Ying Yang 《中国物理 B》2022,31(6):60504-060504
Based on the mean-field theory, we investigate the thermodynamic properties of the two-dimensional (2D) charged spin-1/2 Fermi gas. Landé factor g is introduced to measure the strength of the paramagnetic effect. There is a competition between diamagnetism and paramagnetism in the system. The larger the Landé factor, the smaller the entropy and specific heat. Diamagnetism tends to increase the entropy, while paramagnetism leads to the decrease of the entropy. We find that there exists a critical value of Landé factor for the transition point due to the competition. The entropy of the system increases with the magnetic field when g < 0.58. With the growth of paramagnetism, when g > 0.58, the entropy first decreases with the magnetic field, then reaches a minimum value, and finally increases again. Both the entropy and specific heat increase with the temperature, and no phase transition occurs. The specific heat tends to a constant value at the hightemperature limit, and it approaches to zero at very low temperatures, which have been proved by the analytical calculation. 相似文献
4.
《中国物理 B》2021,30(10):106702-106702
We investigate the polaron and molecular states of a fermionic atom with one-dimensional spin–orbit coupling(SOC)coupled to a three-dimensional spinless Fermi sea. Because of the interplay among the SOC, Raman coupling and spinselected interatomic interactions, the polaron state induced by the spin–orbit coupled impurity exhibits quite unique features. We find that the energy dispersion of the polaron generally has a double-minimum structure, which results in a finite center-of-mass(c.m.) momentum in the ground state, different from the zero-momentum polarons where SOC are introduced into the majority atoms. By further tuning the parameters such as the atomic interaction strength, a discontinuous transition between the polarons with different c.m. momenta may occur, signaled by the singular behavior of the quasiparticle residue and effective mass of the polaron. Meanwhile, the molecular state as well as the polaron-to-molecule transition is also strongly affected by the Raman coupling and the effective Zeeman field, which are introduced by the lasers generating SOC on the impurity atom. We also discuss the effects of a more general spin-dependent interaction and mass ratio. These results would be beneficial for the study of impurity physics brought by SOC. 相似文献
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通过引入描述电荷-磁场和自旋-磁场相互作用竞争关系的自旋因子,研究了磁场和简谐势阱双重约束的二维带电自旋-1/2费米气体的磁性质.结果表明,当自旋因子很小时,系统显示出抗磁性,随着自旋因子的进一步增大,系统逐渐转变为顺磁性.自旋因子的临界值将磁化强度划分为抗磁性区和顺磁性区,临界值随磁场和温度的增大仅发生微小的改变. 相似文献
7.
We study the impurity problem in a Fermi gas of 173Yb atoms near an orbital Feshbach resonance (OFR), where a single moving particle in the 3P0 state interacts with two background Fermi seas of particles in different nuclear states of the ground 1S0 manifold. By employing wave function ansatz to molecule and polaron states, we investigate various properties of the molecule, the attractive polaron, and the repulsive polaron states. In comparison to the case where only one Fermi sea is populated, we find that the presence of an additional Fermi sea acts as an energy shift between the two channels of the OFR. In addition, quantum fluctuations near the Fermi level can also induce sizable effects to various properties of the attractive and repulsive polarons. 相似文献
8.
A study of two-dimensional magnetic polaron 总被引:1,自引:1,他引:0
By using the variational method and anneal simulation, we study in this paper the self-trapped magnetic polaron (STMP) in
two-dimensional anti-ferromagnetic material and the bound magnetic polaron (BMP) in ferromagnetic material. Schwinger angular
momentum theory is applied to changing the problem into a coupling problem of carriers and two types of Bosons. Our calculation
shows that there are single-peak and multi-peak structures in the two-dimensional STMP. For the ferromagnetic material, the
properties of the two-dimensional BMP are almost the same as that in one-dimensional case; but for the anti-ferromagnetic
material, the two-dimensional STMP structure is much richer than the one-dimensional case. 相似文献
9.
We study the linear and nonlinear properties of two-dimensional matter-wave pulses in disk-shaped superfluid Fermi gases.A Kadomtsev-Petviashvili I(KPI) solitary wave has been realized for superfluid Fermi gases in the limited cases of Bardeen-Cooper-Schrieffer(BCS) regime,Bose-Einstein condensate(BEC) regime,and unitarity regime.Onelump solution as well as one-line soliton solutions for the KPI equation are obtained,and two-line soliton solutions with the same amplitude are also studied in the limited cases.The dependence of the lump propagating velocity and the sound speed of two-dimensional superfluid Fermi gases on the interaction parameter are investigated for the limited cases of BEC and unitarity. 相似文献
10.
The problem of bound polarons in quantum dot quantum well (QDQW)
structures is studied theoretically. The eigenfrequencies of bulk
longitudinal optical (LO) and surface optical (SO) modes are derived
in the framework of the dielectric continuum approximation. The
electron--phonon interaction Hamiltonian for QDQW structures is
obtained and the exchange interaction between impurity and
LO-phonons is discussed. The binding energy and the trapping energy
of the bound polaron in CdS/HgS QDQW structures are calculated. The
numerical results reveal that there exist three branches of
eigenfrequencies of surface optical vibration in the CdS/HgS QDQW
structure. It is also shown that the binding energy and the trapping
energy increase as the inner radius of the QDQW structure decreases,
with the outer radius fixed, and the trapping energy takes a major
part of the binding energy when the inner radius is very small. 相似文献
11.
本文利用相干态正交化展开方法, 对两格点两电子Hubbard-Holstein极化子模型的能谱以及动力学特性进行了精确求解. 讨论了耦合强度g、平均声子数n以及电子 初态对纠缠演化特性及系统冯诺依曼熵的影响. 数值计算结果表明: 1)纠缠度随时间的演化呈现出良好的周期性, 当其他的参数固定时, 演化周期随耦合强度g增大逐渐减小, 与平均声子数n无关; 2)系统冯诺依曼熵同电子状态占有率表现出严格的同步演化特性; (3) 在弱耦合强度和低平均声子数下, 初始电子态c2↑+ c2↓+|O>e或c1↑+ c1↓+ |O>e较c1↑+c2↓+—c1↓+ c2↑+具有更大的最大冯诺依曼熵, 并随耦合强度增大、平均声子数的增加而逐渐接近. 相似文献
12.
Xiaoling Jian 《Physics letters. A》2010,374(25):2580-2583
The charged Fermi gas with a small Lande-factor g is expected to be diamagnetic, while that with a larger g could be paramagnetic. We calculate the critical value of the g-factor which separates the dia- and paramagnetic regions. In the weak-field limit, gc has the same value both at high and low temperatures, . Nevertheless, gc increases with the temperature reducing in finite magnetic fields. We also compare the gc value of Fermi gases with those of Boltzmann and Bose gases, supposing the particle has three Zeeman levels σ=±1,0, and find that gc of Bose and Fermi gases is larger and smaller than that of Boltzmann gases, respectively. 相似文献
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以非线性Rosen-Zener隧穿理论为基础, 用平均场近似的方法, 通过考虑高阶非线性项的影响, 研究了非线性两能级系统中费米超流气体的Rosen-Zener隧穿现象. 研究发现粒子间的非线性相互作用能够显著地影响量子隧穿. 分别在快扫描极限和绝热极限的条件下, 解释了Rosen-Zener隧穿现象, 并给出了矩形振荡周期与非线性参数之间的依赖关系. 这为更深入认识费米气体的基本属性提供了理论基础. 相似文献
17.
多体系统的非平衡动力学演化是当前物理学中最具挑战性的问题之一.超冷量子费米原子气体具有较强的可控性,是研究多体非平衡动力学的理想系统,可以用来模拟和理解大爆炸后的早期宇宙、重离子碰撞中产生的夸克-胶子以及核物理等动力学.一般多体系统演化是非常复杂的,往往需要利用对称性来研究.利用Feshbach共振可以制备标度不变的费米原子气体:无相互作用和幺正费米量子气体.当远离平衡态时,可利用普适的指数和函数来刻画,其动力学可以通过对系统的时空演化进行标度变换来识别.本文主要介绍近年来强相互作用超冷费米气体的膨胀动力学研究进展,包括原子气体的各向异性展开、标度动力学和Efimovian膨胀动力学. 相似文献
18.
This paper reports that the ground-state energy of polaron was obtained with strong electron-LO-phonon coupling by using a variational method of the Pekar type in a parabolic quantum dot. Quantum transition is occurred in the quantum system due to the electron-phonon interaction and the influence of temperature. That is the polaron transit from the ground-state to the first-excited state after absorbing a LO-phonon and it causes the change of the polaron lifetime. Numerical calculations are performed and the results illustrate that the ground-state lifetime of the polaron will increase with increasing the ground-state energy of polaron and decrease with increasing the electron-LO-phonon coupling strength, the confinement length of the quantum dot and the temperature. 相似文献
19.
A strongly correlated Fermi system plays a fundamental role in very different areas of physics, from neutron stars, quark–gluon plasmas, to high temperature superconductors. Despite the broad applicability, it is notoriously difficult to be understood theoretically because of the absence of a small interaction parameter. Recent achievements of ultracold trapped Fermi atoms near a Feshbach resonance have ushered in enormous changes. The unprecedented control of interaction, geometry and purity in these novel systems has led to many exciting experimental results, which are to be urgently understood at both low and finite temperatures. Here we review the latest developments of virial expansion for a strongly correlated Fermi gas and their applications on ultracold trapped Fermi atoms. We show remarkable, quantitative agreements between virial predictions and various recent experimental measurements at about the Fermi degenerate temperature. For equations of state, we discuss a practical way of determining high-order virial coefficients and use it to calculate accurately the long-sought third-order virial coefficient, which is now verified firmly in experiments at ENS and MIT. We discuss also virial expansion of a new many-body parameter—Tan’s contact. We then turn to less widely discussed issues of dynamical properties. For dynamic structure factors, the virial prediction agrees well with the measurement at the Swinburne University of Technology. For single-particle spectral functions, we show that the expansion up to the second order accounts for the main feature of momentum-resolved rf-spectroscopy for a resonantly interacting Fermi gas, as recently reported by JILA. In the near future, more practical applications with virial expansion are possible, owing to the ever-growing power in computation. 相似文献
20.
Xi-Wen Guan 《Frontiers of Physics》2012,7(1):8-15
Using solutions of the discrete Bethe ansatz equations, we study in detail the quantum impurity problem of a spin-down fermion immersed into a fully ploarized spin-up Fermi sea with weak attraction. We prove that this impurity fermion in the one-dimensional (1D) fermionic medium behaves like a polaron for weak attraction. However, as the attraction grows, the spin-down fermion binds with one spin-up fermion from the fully-polarized medium to form a tightly bound molecule. Thus it is seen that the system undergos a crossover from a mean field polaron-like nature into a mixture of excess fermions and a bosonic molecule as the attraction changes from weak attraction into strong attraction. This polaron-molecule crossover is universal in 1D many-body systems of interacting fermions. In a thermodynamic limit, we further study the relationship between the Fredholm equations for the 1D spin-1/2 Fermi gas with weakly repulsive and attractive delta-function interactions. 相似文献