Melting of a 2D Quantum Electron Solid in High Magnetic Field

The melting temperature ($T_m$) of a solid is generally determined by the pressure applied to it, or indirectly by its density ($n$) through the equation of state. This remains true even for helium solids\cite{wilk:67}, where quantum effects often lead to unusual properties\cite{ekim:04}. In this letter we present experimental evidence to show that for a two dimensional (2D) solid formed by electrons in a semiconductor sample under a strong perpendicular magnetic field\cite{shay:97} ($B$), the $T_m$ is not controlled by $n$, but effectively by the \textit{quantum correlation} between the electrons through the Landau level filling factor $\nu$=$nh/eB$. Such melting behavior, different from that of all other known solids (including a classical 2D electron solid at zero magnetic field\cite{grim:79}), attests to the quantum nature of the magnetic field induced electron solid. Moreover, we found the $T_m$ to increase with the strength of the sample-dependent disorder that pins the electron solid.Comment: Some typos corrected and 2 references added. Final version with minor editoriol revisions published in Nature Physic

Pressure dependence of Tc and charge transfer in YBa2Cu3Ox (6.35 <= x <= 7) single crystals.

The superconducting critical temperature Tc of YBa2Cu3Ox single crystals (6.35 7) has been measured resistively as a function of pressure P (0P 20 kbar). The initial rate dTc/dP exhibits three distinct regimes, a narrow plateau near 7 with dTc/dP 0.04 K/kbar, a plateau in the range 6.4 6.8, where dTc/dP 0.43 K/kbar, and a maximum value 0.8 K/kbar at 6.35. An analysis of the Tc(x,P) data using a phenomenological model yields a pronounced peak near x=6.8 in dnh(x)/dP, where nh(x) is the change in the hole density in the CuO2 planes relative to the value corresponding to the fully oxygenated sample. © 1992 The American Physical Society

Pressure dependence of Tc and charge transfer in YBa2Cu3Ox (6.35 <= x <= 7) single crystals.

The superconducting critical temperature Tc of YBa2Cu3Ox single crystals (6.35 7) has been measured resistively as a function of pressure P (0P 20 kbar). The initial rate dTc/dP exhibits three distinct regimes, a narrow plateau near 7 with dTc/dP 0.04 K/kbar, a plateau in the range 6.4 6.8, where dTc/dP 0.43 K/kbar, and a maximum value 0.8 K/kbar at 6.35. An analysis of the Tc(x,P) data using a phenomenological model yields a pronounced peak near x=6.8 in dnh(x)/dP, where nh(x) is the change in the hole density in the CuO2 planes relative to the value corresponding to the fully oxygenated sample. © 1992 The American Physical Society

Large pinning forces and matching effects in YBa2Cu3O7-δ thin films with Ba2Y(Nb/Ta)O6 nano-precipitates

The addition of mixed double perovskite Ba(2)Y(Nb/Ta)O(6) (BYNTO) to YBa(2)Cu(3)O(7−δ) (YBCO) thin films leads to a large improvement of the in-field current carrying capability. For low deposition rates, BYNTO grows as well-oriented, densely distributed nanocolumns. We achieved a pinning force density of 25 GN/m(3) at 77 K at a matching field of 2.3 T, which is among the highest values reported for YBCO. The anisotropy of the critical current density shows a complex behavior whereby additional maxima are developed at field dependent angles. This is caused by a matching effect of the magnetic fields c-axis component. The exponent N of the current-voltage characteristics (inversely proportional to the creep rate S) allows the depinning mechanism to be determined. It changes from a double-kink excitation below the matching field to pinning-potential-determined creep above it