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Register a new userMesoscopic Coulomb Supersolid
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When a few tens of charged particles are trapped in a spherical electrostatic potential at low temperature they form concentric shells resembling atoms. These ``artificial atoms can be easily controlled by varying the confinement strength. We analyze such systems for the case that the particles are bosons and find superfluid behavior which even persists in the solid state. This novel state of matter is a mesoscopic supersolid.
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We derive a class of mesoscopic virial equations governing energy partition between conjugate position and momentum variables of individual degrees of freedom. They are shown to apply to a wide range of nonequilibrium steady states with stochastic (Langevin) and deterministic (Nose--Hoover) dynamics, and to extend to collective modes for models of heat-conducting lattices. A generalised macroscopic virial theorem ensues upon summation over all degrees of freedom. This theorem allows for the derivation of nonequilibrium state equations that involve dissipative heat flows on the same footing with state variables, as exemplified for inertial Brownian motion with solid friction and overdamped active Brownian particles subject to inhomogeneous pressure.
We consider mesoscopic fluctuations of the Coulomb drag coefficient $rho_D$ in the system of two separated two-dimensional electron gases. It is shown that at low temperatures sample to sample fluctuations of $rho_D$ exceed its ensemble average. It means that in such a regime the sign of $rho_D$ is random and the temperature dependence almost saturates $rho_D sim 1/sqrt{T}$.
We present the first experimental study of mesoscopic fluctuations of Coulomb drag in a system with two layers of composite fermions, which are seen when either the magnetic field or carrier concentration are varied. These fluctuations cause an alternating sign of the average drag. We study these fluctuations at different temperatures to establish the dominant dephasing mechanism of composite fermions.
We study the interplay between magnetic frustration and itinerant electrons. For example, how does the coupling to mobile charges modify the properties of a spin liquid, and does the underlying frustration favor insulating or conducting states? Supported by Monte Carlo simulations, our goal is in particular to provide an analytical picture of the mechanisms involved. The models under considerations exhibit Coulomb phases in two and three dimensions, where the itinerant electrons are coupled to the localized spins via double exchange interactions. Because of the Hund coupling, magnetic loops naturally emerge from the Coulomb phase and serve as conducting channels for the mobile electrons, leading to doping-dependent rearrangements of the loop ensemble in order to minimize the electronic kinetic energy. At low electron density rho, the double exchange coupling mainly tends to segment the very long loops winding around the system into smaller ones while it gradually lifts the extensive degeneracy of the Coulomb phase with increasing rho. For higher doping, the results are strongly lattice dependent, displaying loop crystals with a given loop length for some specific values of rho, which can melt into another loop crystal by varying rho. Finally, we contrast this to the qualitatively different behavior of analogous models on kagome or triangular lattices.
We show that the Coulomb interaction between two circuits separated by an insulating layer leads to unconventional thermoelectric effects, such as the cooling by thermal current effect, the transverse thermoelectric effect and Maxwells demon effect. The first refers to cooling in one circuit induced by the thermal current in the other circuit. The middle represents electric power generation in one circuit by the temperature gradient in the other circuit. The physical picture of Coulomb drag between the two circuits is first demonstrated for the case with one quantum dot in each circuits and then elaborated for the case with two quantum dots in each circuits. In the latter case, the heat exchange between the two circuits can vanish. Last, we also show that the Maxwells demon effect can be realized in the four-terminal quantum dot thermoelectric system, in which the quantum system absorbs the heat from the high-temperature heat bath and releases the same heat to the low-temperature heat bath without any energy exchange with the two heat baths. Our study reveals the role of Coulomb interaction in non-local four-terminal thermoelectric transport.
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