Download presentation

Presentation is loading. Please wait.

Published byJared Leather Modified over 2 years ago

1
Spin Incoherent Quantum Wires Leon Balents Greg Fiete Karyn Le Hur Frontiers of Science within Nanotechnology, BU August 2005

2
Nanoelectronics Atomic/molecular control –many energy/length scales, individually controllable –can access interesting physics with “emergent” or engineered separation of scales Small size = large Coulomb and large kinetic energy (» e 2 /r, ~ 2 /mr 2 ) Recurring theoretical problem: How to connect nano-structure to meso/macroscopic measuring devices?

3
Quantum Wires Theory: 1DEG Dimensionless gas parameter r s : log r s r s À 1 r s ¿ 1 Luttinger liquid theory FF E k Quasi-Wigner crystal regime “phonons” ZB » F r s 1/2 spin exchange

4
Conductance Experiments Conductance (“0.7”) anomalies in quantum point contacts Similar observations in gated nanotubes Biercuk et al, 2005 Thomas et al, 1996; widely reproduced since. -“plateau” better developed at intermediate temperatures - conductance moves toward G=0.5 (2 e^2/h) in longer constrictions

5
QPC = Low density wire? Matveev (2004) argues: G = e 2 /h (one orbital channel) with ideal metallic leads “Spin incoherent regime” Picture J(x) kBTkBT coherent incoherent - “hot” spin excitations in leads too energetic to penetrate into wire Competing scenarios: Kondo (Meir et al), Ferromagnetism (various) - try to distinguish by other properties?

6
Spectral Properties Introduce electron from outside via tunneling event kFkF -k F kFkF kFkF 2k F A(k, ) k Fermi liquid » 2» 2 Luttinger liquid Spin incoherent liquid » 1/(4g)-1 Cheianov+Zvonarev Greg Fiete+L.B. Notable features: -No coherent single-particle propagation -Change k F ! 2k F : spinless particles at total density -enhancement of local DOS: all spin states ¼ degenerate diverges for g>1/4

7
How to get these results? Cheianov+Zvonarev Our calculation Basic idea: Feynmann world-line path integral - J ¿ T: no crossings of world lines in “time” = ~/k B T action too costly: negligible weight all particles between initial and final point must have same spin prob. of aligned spinsFermi statisticscreate/annihilate particle Can be evaluated by a simple Gaussian integral

8
Some explicit formulae

9
Momentum Resolved Tunneling Experiment: Auslaender et al., Science 2002 Theory: Carpentier et al., PRB 2002 (submitted 2000!) Tserkovnyak et al., PRL 2002 Zulicke & Governale, PRB 2002 E= eV k=eB/mc More recent experiments with one wire gated to low density: k » A(k, ¼ 0) 2 lobes -interplay of disorder and interactions complicated Detailed analysis specific to these experiments: Fiete et al, cond-mat/0501684. (no L.B.!) Steinberg et al, cond-mat/0506812

10
Transport Properties Suppose non-magnetic impurities/defects are introduced inside the spin incoherent wire. - General result: transport within the incoherent region is identical to that of a spinless Luttinger liquid with effective parameters g eff = 2g c and k F,eff =2k F G. Fiete, K. Le Hur, and LB (2005) This can lead to interesting behavior with temperature e.g. Scattering from a single impurity with ½

11
Charge Correlations Low temperature: “Luttinger theorems”: - power-law charge correlations at Q=2k F (LSM, Affleck, Oshikawa) “usually” g c >1/3 : 2k F oscillations longest-range they must disappear when TÀ J may have implications for drag and impurity scattering when T passes through J ? Why 2k_F correlations at all in the Wigner picture? 2 /(4k F ) Heisenberg chain has 1/r staggered dimer fluctuations - spin-phonon coupling leads to period 2 density oscillations

12
Future Directions Experiments to directly observe spin-incoherent physics? - Would like to see coherent spin transport “turn on/off” when T » J e.g very naïve geometry dot wire J À T: RKKY/2-impurity Kondo physics J ¿ T: no communication between spins of dots Spin incoherent physics in ultracold fermions in 1d traps? - Measure hn k i by expansion method hnkihnki k kFkF hnkihnki k2k F T ¿ JTÀ J

13
Theoretical Issues Dynamics at long times: -0

14
Thanks

Similar presentations

OK

D-wave superconductivity induced by short-range antiferromagnetic correlations in the Kondo lattice systems Guang-Ming Zhang Dept. of Physics, Tsinghua.

D-wave superconductivity induced by short-range antiferromagnetic correlations in the Kondo lattice systems Guang-Ming Zhang Dept. of Physics, Tsinghua.

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google

Ppt on c language fundamentals ii What does appt only meanings Ppt on object oriented technologies Ppt on famous business personalities of india Ppt on conservation of momentum in two Ppt on market friendly staten Signal generator and display ppt on ipad Module architecture view ppt on ipad Ppt on job rotation pros Ppt on different solid figures powerpoint