Erratum: Onset of Glassy Dynamics in a Two-Dimensional Electron System in Silicon [Phys. Rev. Lett. 88 , 236401 (2002)]

We report on transport measurements in a thin film of the 2D misfit Cobaltite Ca3Co4O9. Dc magnetoresistance measurements obey the modified variable range hopping law expected for a soft Coulomb gap. When the sample is cooled down, we observe large telegraphic-like fluctuations. At low temperature, these slow fluctuations have non Gaussian statistics, and are stable under a large magnetic field. These results suggest that the low temperature state is a glassy electronic state. Resistance relaxation and memory effects of pure magnetic origin are also observed, but without aging phenomena. This indicates that these magnetic effects are not glassy-like and are not directly coupled to the electronic part. [5]. Furthermore, there is a possibility of frustrated magnetic interactions in a kagome lattice in the CoO 2 layers [6]. Ferrimagnetic or very weak ferromagnetic-like properties are also observed at low temperature [7]. In addition, µ + SR experiments have been interpreted with the presence of a spin density wave at low temperature [8], giving a clue for a gap opening near the Fermi level leading to the observed "Fermi liquid"-insulator transition. Nevertheless, the low temperature transport behavior is not really understood, specially because the ground state of the system is quite complex. The eventual link between all these observations and the measured transport properties has to be clarified. The above mentioned results suggest that low dimensionality, frustration and disorder, together with strong electronic correlations, can be important features for the physical properties of the Ca 3 Co 4 O 9 system. Since they are known to reinforce fluctuations and metastability, one can expect a strong influence on the transport properties. To our knowledge, this has not been verified by the usual macroscopic transport measurements. Because of the statistical averaging, the discrete nature of the underlying "mesoscopic" processes can be masked in a bulk sample but revealed in a smallarea system. In this case, the transport measurements can be used as an efficient probe to bring some light on the ground states of the system [9].In this paper, we report a study of DC magnetotransport properties and of resistance fluctuations in a microbridge of a Ca 3 Co 4 O 9 thin film at low temperature. We particularly focus on the origin (magnetic or electronic) of these resistance fluctuations and relaxation.A 2000Å epitaxial thick film of Ca 3 Co 4 O 9 was used for the measurements. The film was deposited on (0001) Al 2 O 3 using the pulsed laser deposition technique. The details of the optimization, growth conditions and structural characterizations have been described previously [10]. Prior to the transport measurements, a silver layer was firstly deposited via thermal evaporation onto the film, and secondly a gold layer via RF sputtering. Microbridges (L = 200 µm × W = 50 µm) were then patterned with UV photolithography and argon ion etching. Thin aluminum contact wires were finally used to connect the areas to the electrodes w...

supporting

confidence: 85%

Out-of-equilibrium electronic transport properties of a misfit cobaltite thin film

Pautrat¹,

Eng²,

Prellier³

2005

“…The anomalous resistance fluctuations observed in ultrathin granular aluminium films 14 and silicon MOSFETs close to the metal insulator transition 20,21 were also interpreted as indications for glassy behavior. Unfortunately, in these systems, it is difficult to disentangle effects due to intrinsically glassy behavior of interacting electrons from the strong response of the percolating network of hopping electrons to extrinsic slow degrees of freedom.…”

Section: Insulatormentioning

confidence: 99%

“…(20) The density of states at different stages of smearing is shown in Fig 3. Below, we will use the density of states (20) to calculate quantitatively the out of equilibrium conductivity Note that in assumption (i) it is implied that new carriers will occupy sites across the whole film. This is only justified if the film thickness is of the order of the screening length of the sample.…”

Section: Theory Of the Memory Dipmentioning

confidence: 99%

Memory effect in electron glasses: Theoretical analysis via a percolation approach

Lebanon

Müller

2005

We present a theory for the memory effect in electron glasses. In fast gate voltage sweeps it is manifested as a dip in the conductivity around the equilibration gate voltage. We show that this feature, also known as anomalous field effect, arises from the long-time persistence of correlations in the electronic configuration. We argue that the gate voltage at which the memory dip saturates is related to an instability caused by the injection of a critical number of excess carriers. This saturation threshold naturally increases with temperature. On the other hand, we argue that the gate voltage beyond which memory is erased, is temperature independent. Using standard percolation arguments, we calculate the anomalous field effect as a function of gate voltage, temperature, carrier density and disorder. Our results are consistent with experiments, and in particular, they reproduce the observed scaling of the width of the memory dip with various parameters.

“…Our results portray a coherent physical picture, which reveals a quantum critical point at optimum doping (x = xopt), and the formation of an inhomogeneous glassy state at x < xopt. This mechanism is argued to arise as an intrinsic property of doped Mott insulators, and therefore to be largely independent of material quality and level of disorder.Many interesting materials ranging from magnetorestrictive manganite films [1] and field-effect transistors [2,3], to unconventional low dimensional superconductors [4], find themselves close to the metal-insulator transition. In this regime, competition between several distinct ground states [4] produces unusual behavior, displaying striking similarities in a number of different systems.…”

mentioning

confidence: 99%

“…It has been demonstrated in semiconductors [3], ruthanates [17], nickelates [18], other copper oxides [18,19], and manganites [20], where transport experiments indicate that at least some glassy features originate from slow charge dynamics. Further evidence supporting that glassiness in the charge and the spin channels emerge hand-in-hand was recently provided by measurements of the dielectric constant on La 2 Cu 1−x Li x O 4 and La 2−x Sr x N iO 4 [18].…”

mentioning

confidence: 99%

Self-generated electronic heterogeneity and quantum glassiness in the high-temperature superconductors

Panagopoulos

Dobrosavljević

2005

We present a systematic study of the spin and charge dynamics of copper oxide superconductors as a function of carrier concentration x. Our results portray a coherent physical picture, which reveals a quantum critical point at optimum doping (x = xopt), and the formation of an inhomogeneous glassy state at x < xopt. This mechanism is argued to arise as an intrinsic property of doped Mott insulators, and therefore to be largely independent of material quality and level of disorder.Many interesting materials ranging from magnetorestrictive manganite films [1] and field-effect transistors [2,3], to unconventional low dimensional superconductors [4], find themselves close to the metal-insulator transition. In this regime, competition between several distinct ground states [4] produces unusual behavior, displaying striking similarities in a number of different systems. Electronic heterogeneity [1,5] emerges, giving rise to "mesoscopic" coexistence of different ordered phases. Typically, a large number of possible configurations of these local regions have comparable energies, resulting in slow relaxation, aging, and other signatures of glassy systems. Because the stability of such ordering is controlled by doping-dependent quantum fluctuations [6,7] introduced by itinerant carriers, these systems can be regarded as prototypical quantum glasses -a new paradigm of strongly correlated matter.In this Letter we report the emergence and evolution of dynamical heterogeneity and glassy behavior across the phase diagram of the high-transition-temperature (T c ) superconductors (HTS). Based on data of the spin and charge dynamics, we draw a phase diagram (Fig. 1) and propose that self generated glassiness [5] may be a key feature necessary to understand many of the unconventional properties of both the superconducting and the normal state.Glassiness in the pseudo-gap phase. In the archetypal HTS, La 2−x Sr x CuO 4 (LSCO) the parent 2D antiferromagnetic insulator (AFI) La 2 CuO 4 displays a sharp peak in the magnetic susceptibility at the Neel temperature T N = 300K. T N decreases with hole-doping and the transition width broadens (Fig. 2 -upper panel). Concurrently, there is systematic experimental evidence from various techniques and on several HTS that a second freezing transition (T F ) emerges at lower temperatures with the first added holes (Fig. 2) [8,9,10,11,12,13]. At x > 0.02, T N = 0 but the short range order persists [14]: the low-field susceptibility displays a cusp at low temperatures and a thermal hysteresis below, characteristic of a spin glass transition (T g ) (Fig. 2 -upper panel). At T < T g the material displays memory effects like "traditional" spin glasses and is described by an Edwards-Anderson order parameter [15]. Interestingly, it is at this doping range that a pseudogap phase develops [4,16].