Nernst and Seebeck effect in a graphene nanoribbon

The thermoelectric power, including the Nernst and Seebeck effects, in graphene nanoribbon is studied. By using the non-equilibrium Green function combining with the tight-binding Hamiltonian, the Nernst and Seebeck coefficients are obtained. Due to the electron-hole symmetry, the Nernst coefficient is an even function of the Fermi energy while the Seebeck coefficient is an odd function regardless of the magnetic field. In the presence of a strong magnetic field, the Nernst and Seebeck coefficients are almost independent of the chirality and width of the nanoribbon, and they show peaks when the Fermi energy crosses the Landau levels. The height of $n$-th (excluding $n=0$) peak is $[\ln2/|n|]$ for the Nernst effect and is $\ln2/n$ for the Seebeck effect. For the zeroth peak, it is abnormal with height $[2\ln2]$ for the Nernst effect and the peak disappears for the Seebeck effect. When the magnetic field is turned off, however, the Nernst effect is absent and only Seebeck effect exists. In this case, the Seebeck coefficient strongly depends on the chirality of the nanoribbon. The peaks are equidistant for the nanoribbons with zigzag edge but are irregularly distributed for the armchair edge. In particular, for the insulating armchair ribbon, the Seebeck coefficient can be very large near the Dirac point. When the magnetic field varies from zero to large values, the differences among the Seebeck coefficients for different chiral ribbons gradually vanish and the nonzero value of Nernst coefficient appears first near the Dirac point then gradually extents to the whole energy region.Comment: 8 pages, 7 figure

Thermoelectric and Magnetothermoelectric Transport Measurements of Graphene

The conductance and thermoelectric power (TEP) of graphene is simultaneously measured using microfabricated heater and thermometer electrodes. The sign of the TEP changes across the charge neutrality point as the majority carrier density switches from electron to hole. The gate dependent conductance and TEP exhibit a quantitative agreement with the semiclassical Mott relation. In the quantum Hall regime at high magnetic field, quantized thermopower and Nernst signals are observed and are also in agreement with the generalized Mott relation, except for strong deviations near the charge neutrality point

Not so private lives

Not So Private Lives is the first national study to examine same-sex attracted Australians’ preferences for various forms of relationship recognition since the introduction of de facto status for same-sex couples at a federal level. It is also the first major study to investigate preferences for relationship recognition while taking into account the current legal status (in Australia or overseas) of an individual’s same-sex relationship. Findings from the relationship recognition measures of this survey demonstrate that same-sex attracted individuals, like other Australians, differ in the way they prefer their relationships to be formally recognised. However, the results show that the majority of same-sex attracted participants in this survey selected marriage as their personal choice. A federally recognised relationship documented at a registry other than marriage was the second most popular option, and de facto status was the third. The preference for a relationship without any legal status was selected by only 3% of the overall sample. Interestingly, marriage was still the majority choice irrespective of the current legal status of participants’ same-sex relationships (including no legal status). For example, of those currently in a de facto relationship, 55.4% stated they preferred marriage for themselves, 25.6% stated that they preferred a federally recognised relationship other than marriage, 17.7% selected de facto and 1.3% chose no legal status. Participants were also given the opportunity to select which forms of legal relationship recognition they would like to see remain and/or become available in this country for same-sex couples in general. Responses to this measure (which allowed for multiple selections) show that 77.4% would like to see marriage become available as an option, 59.9% would like to see a federally recognised relationship other than marriage be made available and 48% would like to see de facto recognition remain. These numbers indicate that many participants selected multiple options, suggesting that simply having a choice was an important factor. Although the data from this survey indicate that marriage is not for everyone, the majority of same- sex attracted participants in this national survey selected this type of relationship recognition as their personal choice and as a choice to be made available for their fellow same-sex attracted Australians

Non-Adiabatic Spin Transfer Torque in Real Materials

The motion of simple domain walls and of more complex magnetic textures in the presence of a transport current is described by the Landau-Lifshitz-Slonczewski (LLS) equations. Predictions of the LLS equations depend sensitively on the ratio between the dimensionless material parameter $\beta$ which characterizes non-adiabatic spin-transfer torques and the Gilbert damping parameter $\alpha$. This ratio has been variously estimated to be close to 0, close to 1, and large compared to 1. By identifying $\beta$ as the influence of a transport current on $\alpha$, we derive a concise, explicit and relatively simple expression which relates $\beta$ to the band structure and Bloch state lifetimes of a magnetic metal. Using this expression we demonstrate that intrinsic spin-orbit interactions lead to intra-band contributions to $\beta$ which are often dominant and can be (i) estimated with some confidence and (ii) interpreted using the "breathing Fermi surface" model.Comment: 18 pages, 9 figures; submitted to Phys. Rev.

Exact spin dynamics of the 1/r^2 supersymmetric t-J model in a magnetic field

The dynamical spin structure factor S^{zz}(Q,omega) in the small momentum region is derived analytically for the one-dimensional supersymmetric t-J model with 1/r^2 interaction. Strong spin-charge separation is found in the spin dynamics. The structure factor S^{zz}(Q,omega) with a given spin polarization does not depend on the electron density in the small momentum region. In the thermodynamic limit, only two spinons and one antispinon (magnon) contribute to S^{zz}(Q,omega). These results are derived via solution of the SU(2,1) Sutherland model in the strong coupling limit.Comment: 20 pages, 8 figures. Accepted for publication in J.Phys.

Noise properties of two single electron transistors coupled by a nanomechanical resonator

We analyze the noise properties of two single electron transistors (SETs) coupled via a shared voltage gate consisting of a nanomechanical resonator. Working in the regime where the resonator can be treated as a classical system, we find that the SETs act on the resonator like two independent heat baths. The coupling to the resonator generates positive correlations in the currents flowing through each of the SETs as well as between the two currents. In the regime where the dynamics of the resonator is dominated by the back-action of the SETs, these positive correlations can lead to parametrically large enhancements of the low frequency current noise. These noise properties can be understood in terms of the effects on the SET currents of fluctuations in the state of a resonator in thermal equilibrium which persist for times of order the resonator damping time.Comment: Accepted for publication in Phys. Rev.

Effect of Edge Roughness on Electronic Transport in Graphene Nanoribbon Channel Metal Oxide Semiconductor Field-Effect Transistors

Results of quantum mechanical simulations of the influence of edge disorder on transport in graphene nanoribbon metal oxide semiconductor field-effect transistors (MOSFETs) are reported. The addition of edge disorder significantly reduces ON-state currents and increases OFF-state currents, and introduces wide variability across devices. These effects decrease as ribbon widths increase and as edges become smoother. However the bandgap decreases with increasing width, thereby increasing the band-to-band tunneling mediated subthreshold leakage current even with perfect nanoribbons. These results suggest that without atomically precise edge control during fabrication, MOSFET performance gains through use of graphene will be difficult to achieve.Comment: 8 pages, 5 figure

Home accidents amongst elderly people: A locality study in Scotland

Aim The aim of this locality study was to collect information on reported and unreported accidents amongst elderly people living in one locality in Scotland. Method Postal Survey- A postal questionnaire was sent to 3,757 men and women aged 65+ years living in one locality. The questionnaire asked respondents to indicate how many accidents they had experienced in the past twelve months, plus to indicate type and location. Information was gathered on living arrangements, ethnicity, gender, age and deprivation. Respondents were asked if they would be willing to take part in an interview study. Interview Study - One hundred elders who had had at least one accident in the previous twelve months were interviewed. Results Postal Survey - Over a third of the respondents in the postal survey reported having had an accident in the previous twelve months. Bumps and drops and falls were the most common type of accident. Most accidents happened in the kitchen. Women reported more falls than men and those living alone reported more accidents than those living with others. Age was associated with the prevalence of accidents, but the association was somewhat curvilinear, with accidents decreasing with age and then increasing again. Interview Study – Interviewees found it hard to differentiate one accident from another. Considerable reluctance to visit the GP after an accident was noted, with many not attending even for serious accidents. Almost forty percent were ‘very’ distressed after their accident, and a quarter reported a loss of confidence. However, most did not worry about accidents. Few thought that their age, health or medications were a cause of their accidents

Anomalous Fisher-like zeros for the canonical partition function of noninteracting fermions

Noninteracting fermions, placed in a system with a continuous density of states, may have zeros in the $N$-fermion canonical partition function on the positive real $\beta$ axis (or very close to it), even for a small number of particles. This results in a singular free energy, and instability in other thermal properties of the system. In the context of trapped fermions in a harmonic oscillator, these zeros are shown to be unphysical. By contrast, similar bosonic calculations with continuous density of states yield sensible results.Noninteracting fermions, placed in a system with a continuous density of states yield sensible results.Comment: 5 pages and 5 figure

Non-equilibrium Entanglement and Noise in Coupled Qubits

We study charge entanglement in two Coulomb-coupled double quantum dots in thermal equilibrium and under stationary non-equilibrium transport conditions. In the transport regime, the entanglement exhibits a clear switching threshold and various limits due to suppression of tunneling by Quantum Zeno localisation or by an interaction induced energy gap. We also calculate quantum noise spectra and discuss the inter-dot current correlation as an indicator of the entanglement in transport experiments.Comment: 4 pages, 4 figure