Dephasing in Metals by Two-Level Systems in the 2-Channel Kondo Regime

Zawadowski, A.; Delft, Jan von; Ralph, Daniel

doi:10.1103/physrevlett.83.2632

Cited by 115 publications

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“…Kondo physics has been suggested as a possible solution of the dephasing problem in Ref. [16]. The persistent current, of course, will be modified by Kondo correlations, however it is beyond the scope of this paper to estimate this quantitatively.…”

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confidence: 94%

“…However, recently a saturation of the dephasing time has been observed, also after excluding these possibilities [11,12]. Several attempts have been made to explain the low temperature saturation of the dephasing time [13][14][15][16][17]. It has been argued by Altshuler et al [14] that non-equilibrium electromagnetic noise can decohere the electrons without heating them.…”

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confidence: 99%

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Persistent current in metals with a large dephasing rate

Schwab

2000

Eur. Phys. J. B

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In a weakly disordered metal electron interactions are responsible for both decoherence of the quasi-particles as well as for quantum corrections to thermodynamic properties. We consider electrons which are interacting with two-level-systems. We show that the two-level-systems enhance the average equilibrium ("persistent") current in an ensemble of mesoscopic rings. The result supports the recent suggestion that two puzzles in mesoscopic physics may be related: The low temperature saturation of the dephasing time and the high persistent current in rings.PACS numbers: 05.30Fk, 73.23.RaQuantum interference effects play a crucial role in the low temperature properties of normal metals. Prominent examples are weak localization and the associated magnetoresistance. Recently it was suggested [1,2] that two of the unresolved problems in the physics of mesoscopic metals may have a common solution: The large value of the persistent current in mesoscopic rings and the low temperature saturation of the dephasing rate which is seen in magnetoresistance measurements.The first problem is the large value of the persistent current in rings. Lévy et al [3] measured the nonlinear response to a magnetic field of an ensemble of 10 7 mesoscopic copper rings. The measured signal corresponds to a current I ≈ I 0 sin(2πφ/φ 0 ) circulating in each ring. φ is the magnetic flux which penetrates each ring and φ 0 = h/e is the flux quantum. For temperatures in the mK regime the amplitude was |I 0 | ≈ 0.3nA per ring, which is of the order of one elementary charge in the time τ D an electron needs to diffuse around the ring,is the Thouless energy, D is the electron diffusion constant, and L is the circumference of the ring. Similar results were reported in Refs. [1,4]. Theory, when neglecting electron interactions, predicts a current that is of the order I ∼ eδ/h, where δ is the average distance of single particle levels at the Fermi energy [5][6][7]. With the parameters of the experiment [3], δ/k ≈ 0.2mK and E c /k ≈ 25mK, the current obtained is about two orders of magnitude too small. Electron interactions first seemed to improve the situation [8]. For Coulomb interaction it was found that I ∼ eµ * E c /h, where µ * is a dimensionless number that characterizes the strength of the interaction in the Cooper channel. However estimates of µ * gave a value which is an order of magnitude too small when comparing it with the experiment [8]. Surprisingly an enhancement of the current was also reported in presence of a moderate concentration of magnetic impurities [9], with I ∼ e(E c /h)·min(h/τ s , E c )/kT , where 1/τ s is the spin-flip scattering rate. This can become larger than the current coming from the Coulomb interaction, however since the temperature dependence is different from the one observed this mechanism has not been considered as a possible explanation of the experiment in Ref. [3].The second problem concerns the phase coherence of the electrons. Whereas it is expected that the dephasing rate goes to zero in the zero temperature li...

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confidence: 99%

Persistent current in metals with a large dephasing rate

Schwab

2000

Eur. Phys. J. B

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“…This is, to a great extent, due to the problem of the temperature dependence of the electron dephasing time (for a quick introduction of the problem and relevant literature consult Ref. [ 14]). Our paper is also relevant to this problem.…”

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confidence: 99%

Weak localization in InSb thin films heavily doped with lead

2002

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The paper reports on the investigations of the weak localization (WL) effects in 3D (about 2 µm thick) polycrystalline thin films of InSb. The films are closely compensated showing the electron concentration n > 10 16 cm −3 at the total concentration of the donor and acceptor type structural defects Nt > 10 18 cm −3 . Unless Pb-doped, the InSb films do not show any measurable or show very small WL effect at 4.2 K. The Pb-doping to the concentration of the order of 10 18 cm −3 leads to pronounced WL effects below 7 K. In particular, a clearly manifested spin-orbit (SO) scattering is observed. That is ascribed to the large mass of the Pb atoms. From the comparison of the experimental data on temperature dependence of the magnetoresistivity (MR) and sample resistance with the WL theory, the temperature dependence of the phase destroying time τϕ is determined. The determination is performed by fitting theoretical terms obtained from Kawabata's theory to experimental data on magnetoresistance. It is concluded that the dephasing process is connected to three separate interaction processes. The first is due to the SO scatterings and is characterized by temperature-independent relaxation time τso ≃ 10 −12 s. The second is associated with the electronphonon interaction (τi ∼ T −3 ). The third dephasing process is characterized by independent on temperature relaxation time τc = (1 to 7) × 10 −12 s. This relaxation time is tentatively ascribed to inelastic scattering at extended structural defects, like grain boundaries. The resulting time τϕ shows saturation in its temperature dependence for T → 0. The temperature dependence of the resistance of the InSb films can be explained by the electron-electron interaction for T < 1 K, and by the WL effect for T > 2 K. PACS numbers73.20.Fz; 72.15.Rn; 72.10.Fk.

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“…[13,14,15,16]; later work has concentrated on application to coherence and relaxation in tunneling systems (see, eg., refs. [7,17,18,19,20,21]), to decoherence in mesoscopic conductors [22,23], superconducting qubits [7,24], and nanomagnets [25]. It is clear that in the limit of weak coupling to the spin bath, it should be possible to map to an oscillator bath-studies in this limit appear in, eg., refs.…”

Section: : Introductionmentioning

confidence: 99%

Crossovers in spin-boson and central spin models

Stamp

Tupitsyn

2004

Chemical Physics

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We discuss how the crossovers in models like spin-boson model are changed by adding the coupling of the central spin to localised modes-the latter modelled as a 'spin bath'. These modes contain most of the environmental entropy and energy at low T in solid-state systems. We find that the low T crossover between oscillator bath and spin bath dominated decoherence, occurring as one reduces the energy scale of the central spin, is characterised by very low decoherence-we show how this works out in practise in magnetic insulators. We then reconsider the standard quantum-classical crossover in the dynamics of a tunneling system, including both spin and oscillator baths. It is found that the general effect of the spin bath is to broaden the crossover in temperature between the quantum and classical activated regimes. The example of tunneling nanomagnets is used to illustrate this. The oscillator bath models assume that each bath mode is weakly perturbed, and then the description of the bath by oscillators is well known to be correct. Many physical systems are very accurately described by such models [1,3,4,6], and they are central to much of reaction rate chemistry as well. Typically one studies either a particle tunneling from a trapped state to an open continuum of states (the dissipative tunneling problem), or a doublewell system in which a particle has to go from one well to another (the dissipative 2-well problem). One has a range of temperatures in which both activation and tunneling processes are important. Both the width of the crossover regime and the detailed dependence of transition rates, as a function of temperature and applied bias, are of interest [1,5]. In the 2 well problem, the 'quantum limit', where only the 2 lowest levels of the 2-well system are relevant (assuming a weak bias between the wells), has been studied very extensively. This is the 'spin-boson model', in which a 2-level system couples to the oscillator environment.Another interesting application of the spin-boson model is to the problem of qubits in quantum information processing (QUIP). The central issue here is the study of decoherence in the dynamics of the qubit, and how it depends on both simple things like applied fields, temperature, etc., and in a more complex way on the de-

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Dephasing in Metals by Two-Level Systems in the 2-Channel Kondo Regime

Cited by 115 publications

References 48 publications

Persistent current in metals with a large dephasing rate

Persistent current in metals with a large dephasing rate

Weak localization in InSb thin films heavily doped with lead

Crossovers in spin-boson and central spin models

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