187,677 research outputs found
Boltzmann Equation with a Large Potential in a Periodic Box
The stability of the Maxwellian of the Boltzmann equation with a large
amplitude external potential has been an important open problem. In this
paper, we resolve this problem with a large potential in a periodic box
, . We use [1] in framework to
establish the well-posedness and the stability of the Maxwellian
20 K superconductivity in heavily electron doped surface layer of FeSe bulk crystal
A superconducting transition temperature Tc as high as 100 K was recently
discovered in 1 monolayer (1ML) FeSe grown on SrTiO3 (STO). The discovery
immediately ignited efforts to identify the mechanism for the dramatically
enhanced Tc from its bulk value of 7 K. Currently, there are two main views on
the origin of the enhanced Tc; in the first view, the enhancement comes from an
interfacial effect while in the other it is from excess electrons with strong
correlation strength. The issue is controversial and there are evidences that
support each view. Finding the origin of the Tc enhancement could be the key to
achieving even higher Tc and to identifying the microscopic mechanism for the
superconductivity in iron-based materials. Here, we report the observation of
20 K superconductivity in the electron doped surface layer of FeSe. The
electronic state of the surface layer possesses all the key spectroscopic
aspects of the 1ML FeSe on STO. Without any interface effect, the surface layer
state is found to have a moderate Tc of 20 K with a smaller gap opening of 4
meV. Our results clearly show that excess electrons with strong correlation
strength alone cannot induce the maximum Tc, which in turn strongly suggests
need for an interfacial effect to reach the enhanced Tc found in 1ML FeSe/STO.Comment: 5 pages, 4 figure
Baryonic Response of Dense Holographic QCD
The response function of a homogeneous and dense hadronic system to a
time-dependent (baryon) vector potential is discussed for holographic dense QCD
(D4/D8 embedding) both in the confined and deconfined phases. Confined
holographic QCD is an uncompressible and static baryonic insulator at large N_c
and large \lambda, with a gapped vector spectrum and a massless pion.
Deconfined holographic QCD is a diffusive conductor with restored chiral
symmetry and a gapped transverse baryonic current. Similarly, dense D3/D7 is
diffusive for any non-zero temperature at large N_c and large \lambda. At zero
temperature dense D3/D7 exhibits a baryonic longitudinal visco-elastic mode
with a first sound speed \lambda/\sqrt{3} and a small width due to a shear
viscosity to baryon ratio \eta/n_B=\hbar/4. This mode is turned diffusive by
arbitrarily small temperatures, a hallmark of holography.Comment: V2: 47 pages, 7 figures, references added, typos correcte
Structure and correlation effects in semiconducting SrTiO₃
We have investigated the effects of structure change and electron correlation on SrTiO₃ single crystals using angle-resolved photoemission spectroscopy. We show that the cubic to tetragonal phase transition at 105 K is manifested by a charge transfer from in-plane (dyz and dzx) bands to out-of-plane (dxy) band, which is opposite to the theoretical predictions. Along this second-order phase transition, we find a smooth evolution of the quasiparticle strength and effective masses. The in-plane band exhibits a peak-dip-hump lineshape, indicating a high degree of correlation on a relatively large (170 meV) energy scale, which is attributed to the polaron formation
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