1,000 research outputs found
Doping dependence of the vortex-core energy in bilayer films of cuprates
The energy needed to create a vortex core is the basic ingredient to address
the physics of thermal vortex fluctuations in underdoped cuprates. Here we
theoretically investigate its role on the occurrence of the
Beresinskii-Kosterlitz-Thouless transition in a bilayer film with
inhomogeneity. From the comparison with recent measurements of the penetration
depth in two-unit cell thin films of
YCaBaCuO_{7-\d} (YBCO) by Hetel et al. [Nat. Phys.
3, 700 (2007)] we can extract the value of the vortex-core energy , and
show that scales linearly with at low doping.Comment: 4pages, 3 figures. References added, final versio
Spontaneously magnetized Tomonaga-Luttinger liquid in frustrated quantum antiferromagnets
We develop a theory of spontaneously magnetized Tomonaga-Luttinger liquid
(SMTLL) in geometrically frustrated quasi-one-dimensional quantum magnets by
taking an ferrimagnet on a union-jack lattice as an example. We show
that a strong frustration leads to a spontaneous magnetization because of the
ferrimagnetic nature of lattice. Due to the ferrimagnetic order, the local
magnetization has an incommensurate oscillation with the position. We show that
the spontaneously magnetized TLL is smoothly connected to the existence of a
Nambu-Goldstone boson in the canted ferrimagnetic phase of a two-dimensional
frustrated antiferromagnet
Hall effect in strongly correlated low dimensional systems
We investigate the Hall effect in a quasi one-dimensional system made of
weakly coupled Luttinger Liquids at half filling. Using a memory function
approach, we compute the Hall coefficient as a function of temperature and
frequency in the presence of umklapp scattering. We find a power-law correction
to the free-fermion value (band value), with an exponent depending on the
Luttinger parameter . At high enough temperature or frequency the
Hall coefficient approaches the band value.Comment: 7 pages, 3 figure
Thermal rounding of the depinning transition in ultrathin Pt/Co/Pt films
We perform a scaling analysis of the mean velocity of extended magnetic
domain walls driven in ultrathin Pt/Co/Pt ferromagnetic films with
perpendicular anisotropy, as a function of the applied external field for
different film-thicknesses. We find that the scaling of the experimental data
around the thermally rounded depinning transition is consistent with the
universal depinning exponents theoretically expected for elastic interfaces
described by the one-dimensional quenched Edwards-Wilkinson equation. In
particular, values for the depinning exponent and thermal rounding
exponent are tested and the present analysis of the experimental data is
compatible with and , in agreement with numerical
simulations.Comment: 8 pages, 8 figure
Topological transition between competing orders in quantum spin chains
We study quantum phase transitions between competing orders in
one-dimensional spin systems. We focus on systems that can be mapped to a
dual-field double sine-Gordon model as a bosonized effective field theory. This
model contains two pinning potential terms of dual fields that stabilize
competing orders and allows different types of quantum phase transition to
happen between two ordered phases. At the transition point, elementary
excitations change from the topological soliton of one of the dual fields to
that of the other, thus it can be characterized as a topological transition. We
compute the dynamical susceptibilities and the entanglement entropy, which
gives us access to the central charge, of the system using a numerical
technique of infinite time-evolving block decimation and characterize the
universality class of the transition as well as the nature of the order in each
phase. The possible realizations of such transitions in experimental systems
both for condensed matter and cold atomic gases are also discussed.Comment: 8 pages, 7 figure
Spin-charge separation in cold Fermi-gases: a real time analysis
Using the adaptive time-dependent density-matrix renormalization group method
for the 1D Hubbard model, the splitting of local perturbations into separate
wave packets carrying charge and spin is observed in real-time. We show the
robustness of this separation beyond the low-energy Luttinger liquid theory by
studying the time-evolution of single particle excitations and density wave
packets. A striking signature of spin-charge separation is found in 1D cold
Fermi gases in a harmonic trap at the boundary between liquid and
Mott-insulating phases. We give quantitative estimates for an experimental
observation of spin-charge separation in an array of atomic wires
Broadening of the Beresinkii-Kosterlitz-Thouless superconducting transition by inhomogeneity and finite-size effects
We discuss the crucial role played by finite-size effects and inhomogeneity
on the Beresinkii-Kosterlitz-Thouless (BKT) transition in two-dimensional
superconductors. In particular, we focus on the temperature dependence of the
resistivity, that is dominated by superconducting fluctuations above the BKT
transition temperature and by inhomogeneity below it. By means of a
renormalization-group approach we establish a direct correspondence between the
parameter values used to describe the BKT fluctuation regime and the distance
between and the mean-field Ginzburg-Landau transition temperature.
Below a resistive tail arises due to finite-size effect and
inhomogeneity, that reflects also on the temperature dependence of the
superfluid density. We apply our results to recent experimental data in
superconducting LaAlO/SrTiO heterostructures, and we extract several
informations on the microscopic properties of the system from our BKT fitting
parameters. Finally, we compare our approach to recent data analysis presented
in the literature, where the physical meaning of the parameter values in the
BKT formulas has been often overlooked.Comment: 11 pages, 9 figures, final versio
Breakup of the Fermi surface near the Mott transition in low-dimensional systems
We investigate the Mott transition in weakly-coupled one-dimensional (1d)
fermionic chains. Using a generalization of Dynamic Mean Field Theory, we show
that the Mott gap is suppressed at some critical hopping . The
transition from the 1d insulator to a 2d metal proceeds through an intermediate
phase where the Fermi surface is broken into electron and hole pockets. The
quasiparticle spectral weight is strongly anisotropic along the Fermi surface,
both in the intermediate and metallic phases. We argue that such pockets would
look like `arcs' in photoemission experiments.Comment: REVTeX 4, 5 pages, 4 EPS figures. References added; problem with
figure 4 fixed; typos correcte
Spin-charge separation in two-component Bose-gases
We show that one of the key characteristics of interacting one-dimensional
electronic quantum systems, the separation of spin and charge, can be observed
in a two-component system of bosonic ultracold atoms even close to a competing
phase separation regime. To this purpose we determine the real-time evolution
of a single particle excitation and the single-particle spectral function using
density-matrix renormalization group techniques. Due to efficient bosonic
cooling and good tunability this setup exhibits very good conditions for
observing this strong correlation effect. In anticipation of experimental
realizations we calculate the velocities for spin and charge perturbations for
a wide range of parameters
Tunnelling in Organic Superconductors
We present a simple scheme for computing the full current-voltage characteristics for tunnelling experiments within the framework of the non-equilibrium Keldysh Green function formalism. This formalism is flexible enough to address different pairing symmetries combined with magnetic fields at arbitrary bias voltages. We show how to apply these results to probe for the symmetry of the superconducting order parameter in the Bechgaard salts using tunnelling experiment
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