1. Center for Quantum Information ROCHESTER HARVARD CORNELL STANFORD RUTGERS LUCENT TECHNOLOGIES Spin effects and decoherence in high-mobility Si MOSFETs Michael Gershenson Rutgers University in collaboration with Harry Kojima (Rutgers) Vladimir Pudalov (Lebedev Inst.) Grad. Student:Vitaly Podzorov Undergrad. Students: Nick Butch, Taro Sato, Donglai Gong

2. Center for Quantum Information ROCHESTER HARVARD CORNELL STANFORD RUTGERS LUCENT TECHNOLOGIES Quantum computing Spintronics Physics of Strongly Correlated (  dilute) Electron Systems  Spin Effects, Interaction-Driven Magnetic Instabilities Apparent Metal-Insulator Transition in 2D; Ground State of a Strongly Interacting Electron System; Decoherence in a Strongly Interacting System

3. Center for Quantum Information ROCHESTER HARVARD CORNELL STANFORD RUTGERS LUCENT TECHNOLOGIES spin susceptibility g*-factor effective mass decoherence rate B II BB Mixing Chamber of Dilution Fridge Si MOSFET Novel cross-field technique - probing the spin and orbital degrees of freedom of a dilute electron system: High-mobility Si MOSFETs at low temperatures (0.05 – 1 K) and in the crossed magnetic fields (up to 8T)

4. Center for Quantum Information ROCHESTER HARVARD CORNELL STANFORD RUTGERS LUCENT TECHNOLOGIES SdH oscillations in B II - new tool to measure  *, g*, and m* Spin Susceptibility

5. Center for Quantum Information ROCHESTER HARVARD CORNELL STANFORD RUTGERS LUCENT TECHNOLOGIES Giant enhancement of the electron spin susceptibility in low-density 2DEG with decreasing carrier density, the el.-el. interactions are strongly enhanced Scaling Analysis: the apparent metal- insulator transition in 2D is not accompanied with a magnetic instability. This, however, does not exclude possibility of a magnetic transition at n  5x10 10 cm -2 an apparent 2D MIT M. Gershenson, an invited talk at the APS March Meeting, 2001; an invited talk at the EP2DS Conf, Physica E V. Pudalov et al., cond-mat/0105081, submitted to PRL; cond-mat/0110160; cond-mat/0201001

6. Center for Quantum Information ROCHESTER HARVARD CORNELL STANFORD RUTGERS LUCENT TECHNOLOGIES Decoherence in a strongly interacting system Weak Localization MR L  =  D    L H The weak localization corrections in the 2DEG with r s up to 8 (r s, the ratio of the Coulomb energy to the kinetic energy, characterizes the strength of el.-el. interactions)

7. Center for Quantum Information ROCHESTER HARVARD CORNELL STANFORD RUTGERS LUCENT TECHNOLOGIES a strongly interacting system – is still a Fermi-liquid system The first (diffusive) term becomes comparable to the second (ballistic) term when T  ~ 1 The singlet + triplet channels – Narozhny, Zala, Aleiner, ‘02 Decoherence in two dimensions due to el.-el. interactions

8. Center for Quantum Information ROCHESTER HARVARD CORNELL STANFORD RUTGERS LUCENT TECHNOLOGIES Effect of the parallel magnetic field on decoherence In strong fields,   is reduced by an order of magnitude! M. Gershenson, an invited talk at the Conference “Macroscopic Quantum Coherence and Dissipation”, Aspen, February 2002.

9. Center for Quantum Information ROCHESTER HARVARD CORNELL STANFORD RUTGERS LUCENT TECHNOLOGIES Mechanisms of enhancement of the decoherence rate in B II  due to the Si-SiO 2 interface roughness an electron picks up a random Berry’s phase  the electron sees uniform B II as random B  Mensz at al., Appl. Phys. Lett. 50, 603 (1987) Mensz and Wheeler, Phys. Rev. B 35, 2844 (1987) Mathur and Baranger, Phys. Rev. B 64, 235325 (2001)  a) asymmetric scatterers with respect to the middle of a quantum well + b) B II, which breaks the time-reversal symmetry and couples different sub-bands of size quantization Fal’ko, J. Phys. Condens Matter 2, 3797 (1990) Meyer, Altland, and Altshuler, cond-mat/0105623

10. Center for Quantum Information ROCHESTER HARVARD CORNELL STANFORD RUTGERS LUCENT TECHNOLOGIES M. Gershenson et al. Appl. Phys. Lett. 79, 2049 (2001) Electron-phonon coupling in low-dimensional conductors cooling of mesoscopic systems promising applications in hot-electron devices operating at T < 1 K The electron cooling time for ultra-thin Hf and Ti films  - Hf, d = 25nm, R  = 38   - Ti, d = 20nm, R  = 14.7  ultra-long (up to 1 s !!) el.-ph. scattering time good agreement with the q T l << 1 theory sensitivity of state-of-the-art FIR bolometers can be improved by ~ 10 2

11. Center for Quantum Information ROCHESTER HARVARD CORNELL STANFORD RUTGERS LUCENT TECHNOLOGIES Future directions: Organic-molecular-crystal based FETs (unique opportunity to explore the ultra-strong interaction regime, r s ~ 100) Quantum dots in Si Nano-sensors and nano-calorimeters based on hot-electron effects at low temperatures New undergraduate course in nanoscience and quantum computing Facility for nano-fabrication Hiring in nano-science + quantum computing