Evidence for Charge Glasslike Behavior in Lightly DopedLa2−xSrxCuO4at Low Temperatures

Abstract

A c-axis magnetotransport and resistance noise study in La1.97Sr0.03CuO4 reveals clear signatures of glassiness, such as hysteresis, memory, and slow, correlated dynamics, but only at temperatures (T ) well below the spin glass transition temperature Tsg. The results strongly suggest the emergence of charge glassiness, or dynamic charge ordering, as a result of Coulomb interactions. PACS numbers: 74.72.Dn, 72.70.+m, 75.50.Lk The role of heterogeneities observed in most holedoped high-temperature superconductors (HTS) is one of the major open issues in the field [1,2]. In weakly doped Mott insulators, such as HTS, charge heterogeneities are expected to arise due to the existence of several competing ground states [3], and may be even to exhibit glassy dynamics [4]. Even a small amount of disorder may favor glassiness over various static charge-ordered states [5]. Experiments in hole-doped HTS suggest [6,7,8,9] that glassiness of both spins and charges emerges with the first added holes and evolves with doping x. While spin glass (SG) behavior is well established at low T , the evidence for glassy freezing of charges is not conclusive. Hence, alternative, bulk probes of charge dynamics are needed to explore the nature of the ground state. We present a novel study of the charge dynamics in a lightly doped La 2−x Sr x CuO 4 (LSCO) using a combination of transport and noise spectroscopy that proved to be a powerful probe of dynamics in other glasses [10,11]. We find several clear signatures of glassiness at T ≪ T sg . The data strongly suggest that the doped holes form a dynamically ordered, cluster glass as a result of Coulomb interactions.In LSCO, the prototypical cuprate HTS, the threedimensional (3D) long range antiferromagnetic (AF) order of the parent compound is destroyed above x ≈ 0.02, but 2D short range AF correlations persist [12]. In particular, as a result of hole doping, CuO 2 (ab) planes develop a pattern of AF domains that are separated by antiphase boundaries [13,14,15]. Since the Dzyaloshinskii-Moriya interaction induces slight canting of the spins in CuO 2 planes towards the c axis, there is a weak ferromagnetic (FM) moment in the bc plane associated with each AF domain, such that the direction of the FM moment is uniquely linked to the phase of the AF order [15,16]. The interplane exchange favors staggered ordering of those FM moments in the c direction. At low enough T < T sg (x), the system freezes into a SG [12,14,15] that extends into the superconducting (SC) phase for x > 0.05[17] up to optimal doping [18] [ Fig. 1(a)]. Various experiments on lightly doped LSCO (e.g. Refs. [6,7]), including transport studies [19], were interpreted in terms of the hole-poor AF domains separated by the hole-rich regions in CuO 2 planes, with infrared studies being inconsistent with the notion of static charge ordering [8].We report an extensive study of the low-T (T ∼ 1 K and below) c-axis magnetotransport and low-frequency resistance (R) noise in LSCO with x = 0.03 [ Fig. 1(a)]. Such lightly doped samples a...

Large Room Temperature Magneto-Resistance in Magnetically Disordered Fe&lt;sub&gt;1.5&lt;/sub&gt;Ti&lt;sub&gt;0.5&lt;/sub&gt;O&lt;sub&gt;3-δ&lt;/sub&gt; Thin Films

“…The negative magneto-resistance in case of VRH mechanism has been reported for Fe 2 O 3 where similar to FTO conductivity is by Fe 3+ , Fe 2+ pairs and also in number of magnetic semiconductors and oxide materials [32]- [37].…”

Insulating and metallic spin glass in Ni-dopedKxFe2−ySe2single crystals

“…46 High degree of crystalline disorder in I4/mmm and in I4/m phase results in insulating or bad metal magnetic glass state that borders superconducting region, similar to copper oxides. 47,48 In the insulating region of K x Fe 2−δ−y Ni y Se 2 single crystal alloys ground state phase diagram (Fig. 4(b)), freezing temperatures T f of the magnetic spin glass are higher (∼ 60 K) when compared to metallic regions (∼ 20 K) (y>1.13(1)).…”

Hall effect in quantum critical charge-cluster glass

“…Therefore, we have to consider more exotic mechanisms, beyond the nearly free electron model. In particular, we should contemplate the Hall effect in a charge-, spin-, or superconducting vortex-glass state, all of which were reported to occur in underdoped cuprates (6)(7)(8)(9)(10)(11)(12). Although regrettably a broadly accepted quantitative theory of these phenomena is still missing, we can discriminate between these three glassy states based on qualitative arguments, as follows.…”

“…However, in the vicinity of the quantum critical point, the physics gets more complex because of the intrinsic inhomogeneity induced by strong localization and significant spin, charge, and phase fluctuations (6)(7)(8)(9)(10)(11)(12). As a result, spin glass (6-9), charge glass (or charge-cluster glass) (10,11), and superconducting vortex liquid/glass (12) all occur in the x-H-T phase diagram near the SIT. For instance, erratic switching in the (longitudinal) resistivity ρ has been observed (11) at very low temperature in two underdoped superconducting LSCO samples, and was taken as a signature of the charge-glass state.…”

“…Next, we show that measuring the transverse (Hall) resistivity, ρ H , rather than the longitudinal resistivity ρ, is a much more sensitive probe of charge fluctuations. The charge-cluster glass (CCG) can be envisioned as entailing domains of more-or-less localized charges, which fluctuate greatly in time and space (9)(10)(11). The fact that switching can be observed at all in the dc resistance, and even more that it is slow, indicates that at least some of these domains must be relatively large.…”