[ # ] these authors contributes equally to this work Keywords: resistive switching, non-volatile memory, Mott insulator, metal-insulator transitionThe fundamental building blocks of modern silicon-based microelectronics, such as double gate transistors in non-volatile Flash memories, are based on the control of electrical resistance by electrostatic charging. Flash memories could soon reach their miniaturization limits mostly because reliably keeping enough electrons in an always smaller cell size will become increasingly difficult [1] . The control of electrical resistance at the nanometer scale therefore requires new concepts, and the ultimate resistance-change device is believed to exploit a purely electronic phase change such as the Mott insulator to insulator transition [ 2 ].Here we show that application of short electric pulses allows to switch back and forth between an initial high-resistance insulating state ("0" state) and a low-resistance "metallic" state ("1" state) in the whole class of Mott Insulator compounds AM 4 X 8 (A = Ga, Ge; M= V, Nb, Ta; X = S, Se). We found that electric fields as low as 2 kV/cm induce an electronic phase change in these compounds from a Mott insulating state to a metallic-like state. Our results suggest that this transition belongs to a new class of resistive switching and might be explained by recent theoretical works predicting that an insulator to metal transition can be achieved by a simple electric field in a Mott Insulator [3,4,5] . This new type of resistive switching has potential to build up a new class of Resistive Random Access Memory (RRAM) with fast writing/erasing times (50 ns to 10 µs) and resistance ratios R/R of the order of 25% at room temperature.

We report a study of the geometrically frustrated magnetic material Tb 2 Sn 2 O 7 by the positive muonspin relaxation technique. No signature of a static magnetically ordered state is detected while neutron magnetic reflections are observed in agreement with a published report. This is explained by the dynamical nature of the ground state of Tb 2 Sn 2 O 7 : the Tb 3 magnetic moment characteristic fluctuation time is ' 10 ÿ10 s. The strong effect of the magnetic field on the muon-spin-lattice relaxation rate at low fields indicates a large field-induced increase of the magnetic density of states of the collective excitations at low energy. DOI: 10.1103/PhysRevLett.96.127202 PACS numbers: 75.40.ÿs, 75.25.+z, 76.75.+i Magnetic materials with antiferromagnetically coupled spins located on triangular motifs exhibit geometrical magnetic frustration because their spatial arrangement is such that it prevents the simultaneous minimization of all the interaction energies [1]. The frustration, which leads to a highly degenerate ground state, forbids magnetic order to occur. Perturbations to the nearest-neighbor exchange interaction, such as exchange interactions extending beyond nearest-neighbor magnetic atoms, dipole coupling, or magnetic anisotropy, are believed to be responsible for the magnetic order observed in some compounds [2]. Typical examples are given by the spinel structure oxide [6]. A prerequisite for understanding the unanticipated behavior of these latter systems is a careful characterization of their dynamical properties.Here we show that positive muon-spin relaxation ( SR) and ND results in the ordered phase of Tb 2 Sn 2 O 7 can be simultaneously accounted for only if the Tb 3 moments are strongly dynamical. An independent and consistent time scale is obtained from a careful analysis of the neutron data. In addition, the initial strong and counterintuitive increase of the muon relaxation rate when a magnetic field is applied indicates an increase of the density of magnetic excitations at very low energy.Tb 2 Sn 2 O 7 crystallizes with the cubic space group Fd 3m. Rietveld refinements of powder x-ray and ND patterns yield the lattice constant a 10:426 A and the free position parameter allowed by the space group for the 48f site occupied by oxygen, x 0:336 [6]. Magnetic measurements point to a magnetic transition at 0.87 K and to strong antiferromagnetic interactions as deduced from the large and negative Curie-Weiss constant CW ÿ12 K [13]. Powder ND indicates a structure with both ferromagnetic and antiferromagnetic components below T sr 1:3 1 K where short-range magnetic correlations which are not liquidlike appear [6]. A steep increase of the Tb 3 magnetic moment Tb and correlation length L c is observed around T lr 0:87 K, where a peak is seen in the temperature dependence of the specific heat C p T . We present below (i) C p T data recorded using a dynamic adiabatic technique, (ii) ND measurements carried out at the cold neutron powder diffractometer DMC of the SINQ facility at the Paul Scherrer I...

Experimental evidence of a nonvolatile electric-pulse-induced insulator-to-metal transition and possible superconductivity in the Mott insulator GaTa4 Se8 is reported. Scanning tunneling microscopy experiments show that this unconventional response of the system to short electric pulses arises from a nanometer-scale electronic phase separation generated in the bulk material.