Physical Review Letters

Zhang, Qingteng ; Ponomareva, I

doi: 10.1103/PhysRevLett.105.147602pmid: 21230867

A microscopic approach based on the first-principles effective Hamiltonian is developed to study the polarization response in temperature-graded ferroelectrics. This approach has been applied to the case of ( Ba 0.75 Sr 0.25 ) TiO 3 alloy. A comparison of the computational results with available experimental data attests to the remarkable accuracy of the present approach. Our computations reveal a strong anisotropy in the response of polarization to the temperature gradient (TG). In particular, the polarization offset along the direction of TG is an order of magnitude lower than in the perpendicular direction. The large as well as the small TGs are considered and found to yield qualitatively different polarization field responses. Among other striking findings are (i) the coexistence of different phases in chemically homogeneous regions, (ii) formation of low-symmetry phases, and (iii) thermally controlled polarization rotation.

Lucamarini, Marco ; Kumar, Rupesh ; Di Giuseppe, Giovanni ; Vitali, David ; Tombesi, Paolo

doi: 10.1103/PhysRevLett.105.140504pmid: 21230820

An asymmetric preparation of the quantum states sent through a noisy channel can enable a new way to monitor and actively compensate the channel noise. The paradigm of such an asymmetric treatment of quantum information is the Bennett 1992 protocol, in which the counts in the two separate bases are in direct connection with the channel noise. Using this protocol as a guiding example, we show how to correct the phase drift of a communication channel without using reference pulses, interruptions of the quantum transmission, or public data exchanges.

Oberdorfer, Bernd ; Steyskal, Eva-Maria ; Sprengel, Wolfgang ; Puff, Werner

doi: 10.1103/PhysRevLett.105.146101pmid: 21230846

A high-intensity positron beam is used for specific in situ monitoring of thermally activated fast defect annealing in Cu and Ni on a time scale of minutes. The atomistic technique of positron-electron annihilation is combined with macroscopic high-precision length-change measurements under the same thermal conditions. The combination of these two methods as demonstrated in this case study allows for a detailed analysis of multistage defect annealing in solids distinguishing vacancies, dislocations, and grain growth.

Dalmonte, M; Pupillo, G; Zoller, P

doi: 10.1103/PhysRevLett.105.140401pmid: 21230815

We study one-dimensional fermionic and bosonic gases with repulsive power-law interactions 1 / | x | β , with β > 1 , in the framework of Tomonaga-Luttinger liquid (TLL) theory. We obtain an accurate analytical expression linking the TLL parameter to the microscopic Hamiltonian, for arbitrary β and strength of the interactions. In the presence of a small periodic potential, power-law interactions make the TLL unstable towards the formation of a cascade of lattice solids with fractional filling, a “Luttinger staircase.” Several of these quantum phases and phase transitions are realized with ground state polar molecules and weakly bound magnetic Feshbach molecules.

Kuroda, K; Ye, M; Kimura, A; Eremeev, S. V; Krasovskii, E. E; Chulkov, E. V; Ueda, Y. V; Miyamoto, K. V; Okuda, T. V; Shimada, K. V; Namatame, H. V; Taniguchi, M. V

doi: 10.1103/PhysRevLett.105.146801

Pellegrini, Franco ; Santoro, Giuseppe E; Tosatti, Erio E

doi: 10.1103/PhysRevLett.105.146103pmid: 21230848

We identify the mechanism of energy dissipation relevant to spin-sensitive nanomechanics including the recently introduced magnetic exchange force microscopy, where oscillating magnetic tips approach surface atomic spins. The tip-surface exchange couples spin and atom coordinates, leading to a spin-phonon problem with Caldeira-Leggett–type dissipation. In the overdamped regime, that can lead to a hysteretic flip of the local spin with a large spin-dependent dissipation, even down to the very low experimental tip oscillation frequencies, describing recent observations for Fe tips on NiO. A phase transition to an underdamped regime with dramatic drop of magnetic tip dissipation should in principle be possible by tuning tip-surface distance.

Soifer, H; Botheron, P; Shafir, D; Diner, A; Raz, O; Bruner, B. D; Mairesse, Y. D; Pons, B. D; Dudovich, N. D

doi: 10.1103/PhysRevLett.105.143904pmid: 21230832

We study high-order harmonic generation in aligned molecules close to the ionization threshold. Two distinct contributions to the harmonic signal are observed, which show very different responses to molecular alignment and ellipticity of the driving field. We perform a classical electron trajectory analysis, taking into account the significant influence of the Coulomb potential on the strong-field-driven electron dynamics. The two contributions are related to primary ionization and excitation processes, offering a deeper understanding of the origin of high harmonics near the ionization threshold. This Letter shows that high-harmonic spectroscopy can be extended to the near-threshold spectral range, which is in general spectroscopically rich.

Berg, Erez ; Fradkin, Eduardo ; Kivelson, Steven A

doi: 10.1103/PhysRevLett.105.146403pmid: 21230852

We show, using density-matrix renormalization-group calculations complemented by field-theoretic arguments, that the spin-gapped phase of the one dimensional Kondo-Heisenberg model exhibits quasi-long-range superconducting correlations only at a nonzero momentum. The local correlations in this phase resemble those of the pair-density-wave state which was recently proposed to describe the phenomenology of the striped ordered high-temperature superconductor La 2 - x Ba x CuO 4 , in which the spin, charge, and superconducting orders are strongly intertwined.

Wu, Hua ; George, Richard E; Wesenberg, Janus H; Mølmer, Klaus H; Schuster, David I; Schoelkopf, Robert J; Itoh, Kohei M; Ardavan, Arzhang M; Morton, John J; Briggs, G. Andrew

doi: 10.1103/PhysRevLett.105.140503pmid:

Campisi, Michele ; Talkner, Peter ; Hänggi, Peter

doi: 10.1103/PhysRevLett.105.140601pmid: 21230821

It is shown that quantum fluctuation theorems remain unaffected if measurements of any kind and number of observables are performed during the action of a force protocol. That is, although the backward and forward probabilities entering the fluctuation theorems are both altered by these measurements, their ratio remains unchanged. This observation allows us to describe the measurement of fluxes through interfaces and, in this way, to bridge the gap between the current theory, based on only two measurements performed at the beginning and end of the protocol, and experiments that are based on continuous monitoring.