scholarly journals Strongly correlated superfluid order parameters from dc Josephson supercurrents

Science ◽  
2020 ◽  
Vol 369 (6499) ◽  
pp. 84-88 ◽  
Author(s):  
W. J. Kwon ◽  
G. Del Pace ◽  
R. Panza ◽  
M. Inguscio ◽  
W. Zwerger ◽  
...  
Keyword(s):  
Order Parameters ◽  
Current Phase ◽  
Einstein Condensation ◽  
Strongly Correlated ◽  
Strong Correlations ◽  
Atomic Systems ◽  
Zero Resistance ◽  
Resistance State ◽  
Sinusoidal Current ◽  
Bose Einstein

The direct-current (dc) Josephson effect provides a phase-sensitive tool for investigating superfluid order parameters. We report on the observation of dc Josephson supercurrents in strongly interacting fermionic superfluids across a tunneling barrier in the absence of any applied potential difference. For sufficiently strong barriers, we observed a sinusoidal current-phase relation, in agreement with Josephson’s seminal prediction. We mapped out the zero-resistance state and its breakdown as a function of junction parameters, extracting the Josephson critical current behavior. By comparing our results with an analytic model, we determined the pair condensate fraction throughout the Bardeen-Cooper-Schrieffer–Bose-Einstein condensation crossover. Our work suggests that coherent Josephson transport may be used to pin down superfluid order parameters in diverse atomic systems, even in the presence of strong correlations.

scholarly journals What is strange about high-temperature superconductivity in cuprates?

2017 ◽  
Vol 31 (25) ◽  
pp. 1745005
Author(s):  
I. Božović ◽  
X. He ◽  
J. Wu ◽  
A. T. Bollinger
Keyword(s):  
Phase Diagram ◽  
Cuprate Superconductors ◽  
High Temperature Superconductivity ◽  
Einstein Condensation ◽  
Strongly Correlated ◽  
Bose Einstein Condensation ◽  
Ultimate Question ◽  
Underdoped Cuprates ◽  
Bose Einstein ◽  
Superconducting Parameters

Cuprate superconductors exhibit many features, but the ultimate question is why the critical temperature ([Formula: see text]) is so high. The fundamental dichotomy is between the weak-pairing, Bardeen–Cooper–Schrieffer (BCS) scenario, and Bose–Einstein condensation (BEC) of strongly-bound pairs. While for underdoped cuprates it is hotly debated which of these pictures is appropriate, it is commonly believed that on the overdoped side strongly-correlated fermion physics evolves smoothly into the conventional BCS behavior. Here, we test this dogma by studying the dependence of key superconducting parameters on doping, temperature, and external fields, in thousands of cuprate samples. The findings do not conform to BCS predictions anywhere in the phase diagram.

scholarly journals An ideal Josephson junction in an ultracold two-dimensional Fermi gas

Science ◽  
2020 ◽  
Vol 369 (6499) ◽  
pp. 89-91 ◽  
Author(s):  
Niclas Luick ◽  
Lennart Sobirey ◽  
Markus Bohlen ◽  
Vijay Pal Singh ◽  
Ludwig Mathey ◽  
...  
Keyword(s):  
Josephson Junction ◽  
High Temperature Superconductors ◽  
Fermi Gas ◽  
Current Phase ◽  
Strongly Correlated ◽  
Two Dimensional ◽  
Weakly Bound ◽  
Ideal Model System ◽  
Sinusoidal Current ◽  
2D Fermi Gas

The role of reduced dimensionality in high-temperature superconductors is still under debate. Recently, ultracold atoms have emerged as an ideal model system to study such strongly correlated two-dimensional (2D) systems. Here, we report on the realization of a Josephson junction in an ultracold 2D Fermi gas. We measure the frequency of Josephson oscillations as a function of the phase difference across the junction and find excellent agreement with the sinusoidal current phase relation of an ideal Josephson junction. Furthermore, we determine the critical current of our junction in the crossover from tightly bound molecules to weakly bound Cooper pairs. Our measurements clearly demonstrate phase coherence and provide strong evidence for superfluidity in a strongly interacting 2D Fermi gas.

scholarly journals ABSENCE OF BCS CONDENSATION OF ATOMS IN A REPULSIVE FERMI GAS OF ATOMS

2008 ◽  
Vol 22 (01) ◽  
pp. 9-16
Author(s):  
FUXIANG HAN ◽  
HAILING LI ◽  
MINGHAO LEI ◽  
E. WU
Keyword(s):  
Fermi Gas ◽  
Order Parameters ◽  
The Self ◽  
Einstein Condensation ◽  
Cooper Pairs ◽  
Path Integral Representation ◽  
Body Interaction ◽  
Self Consistent ◽  
Atom Interaction ◽  
Bose Einstein

Bose–Einstein condensation of molecules and BCS condensation of Cooper pairs of atoms in an ultra-cold Fermi gas of atoms with a repulsive two-body interaction are studied by using the path integral representation of the grand partition function. From the self-consistent equations obtained in the present work for the order parameters, we have found that BCS condensation of atoms cannot occur in such a Fermi gas of atoms and that the condensate observed experimentally is composed of condensed molecules or possibly of preformed Cooper pairs. To substantiate our conclusions from the self-consistent equations for the order parameters, the effective atom–atom interaction mediated through molecules has also been computed with the Foldy–Wouthuysen transformation and has been found to be repulsive, which implies a net repulsive two-body interaction between atoms and hence the absence of BCS condensation of atoms.

ANTHONY LEGGETT: FEENBERG MEDALIST 1999 CONDENSED MATTER AS A TEST-BED FOR FUNDAMENTAL QUANTUM MECHANICS

2001 ◽  
Vol 15 (10n11) ◽  
pp. 1305-1311 ◽  
Author(s):  
C. E. CAMPBELL ◽  
J. W. CLARK ◽  
E. KROTSCHECK ◽  
L. P. PITAEVSKII
Keyword(s):  
Quantum Coherence ◽  
High Temperature Superconductivity ◽  
Einstein Condensation ◽  
Test Bed ◽  
Many Body ◽  
Atomic Systems ◽  
Liquid Theory ◽  
Macroscopic Quantum Coherence ◽  
Key Aspects ◽  
Bose Einstein

The Eugene Feenberg Medal is awarded to Anthony J. Leggett in recognition of his seminal contributions to Many-Body Physics, including the explanation of the remarkable properties of superfluid 3 He in the millikelvin regime, important results in Fermi-liquid theory applied to metals, fundamental new insights into macroscopic quantum coherence, elucidation of key aspects of high-temperature superconductivity, and pioneering studies of the implications of Bose-Einstein condensation in atomic systems.

scholarly journals Metastable Bose-Einstein condensation in a strongly correlated optical lattice

2015 ◽  
Vol 91 (2) ◽  
Author(s):  
David McKay ◽  
Ushnish Ray ◽  
Stefan Natu ◽  
Philip Russ ◽  
David Ceperley ◽  
...  
Keyword(s):  
Optical Lattice ◽  
Einstein Condensation ◽  
Strongly Correlated ◽  
Bose Einstein Condensation ◽  
Bose Einstein

scholarly journals Bose-Einstein condensation of correlated atoms in a trap

2019 ◽  
Vol 11 ◽  
Author(s):  
Ch. C. Moustakidis ◽  
S. E. Massen
Keyword(s):  
Kinetic Energy ◽  
Density Distribution ◽  
Einstein Condensation ◽  
Body Density ◽  
Atomic Systems ◽  
Bose Einstein Condensation ◽  
Occupation Numbers ◽  
The One ◽  
Bose Einstein ◽  
Analytical Expressions

The Bose-Einstein condensation of correlated atoms in a trap is studied by examining the effect of inter-particle correlations to one-body properties of atomic systems at zero temperature using a simplified formula for the correlated two body density distribution. Analytical expressions for the density distribution and rms radius of the atomic systems are derived using four different expressions of Jastrow type correlation function. In one case, in addition, the one-body density matrix, momentum distribution and kinetic energy are calculated analytically, while the natural orbitals and natural occupation numbers are also predicted in this case. Simple approximate expressions for the mean square radius and kinetic energy are also given.

Field-induced Bose–Einstein condensation of a strongly correlated spin liquid in BaCuSi2O6

2005 ◽  
Vol 359-361 ◽  
pp. 1369-1371
Author(s):  
M. Jaime ◽  
V. Correa ◽  
N. Harrison ◽  
C.D. Batista ◽  
N. Kawashima ◽  
...  
Keyword(s):  
Einstein Condensation ◽  
Spin Liquid ◽  
Strongly Correlated ◽  
Bose Einstein Condensation ◽  
Bose Einstein

scholarly journals SIMULTANEOUS ONSET OF CONDENSATION OF MOLECULES AND ATOMS IN AN ATTRACTIVE FERMI GAS OF ATOMS

2007 ◽  
Vol 21 (01) ◽  
pp. 51-58
Author(s):  
FUXIANG HAN ◽  
MINGHAO LEI ◽  
E WU
Keyword(s):  
Critical Temperature ◽  
Fermi Gas ◽  
Order Parameters ◽  
Einstein Condensation ◽  
Grand Partition Function ◽  
Path Integral Representation ◽  
Hartree Fock ◽  
Bogoliubov Approximation ◽  
The Common ◽  
Bose Einstein

The self-consistent equations for the order parameters of Bose–Einstein condensation (BEC) of molecules and Bardeen–Cooper–Schrieffer (BCS) condensation of atoms in a Fermi gas of atoms with an attractive two-body interaction between atoms have been derived within the Hartree–Fock–Bogoliubov approximation from the path integral representation of the grand partition function. We have found that the order parameters for BEC and BCS are proportional to each other, which implies that BEC and BCS onsets simultaneously. We have also found that the common critical temperature of BEC and BCS increases as the average number of molecules increases and that the atom-molecule coupling enhances the common critical temperature.

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