Two-channel Kondo physics in two-impurity Kondo models

We consider the non-Fermi liquid quantum critical state of the spin-S two-impurity Kondo model, and its potential realization in a quantum dot device. Using conformal field theory (CFT) and the numerical renormalization group (NRG), we show the critical point to be identical to that of the two-channel Kondo model with additional potential scattering, for any spin-S. Distinct conductance signatures are shown to arise as a function of device asymmetry; with the `smoking gun' square-root behavior, commonly believed to arise at low-energies, dominant only in certain regimes.Comment: 4.5 pages (with 3 figures) + 9 pages (with 4 figures) supplementary materia

Majorana Fermions in Strongly Interacting Helical Liquids

Majorana fermions were proposed to occur at edges and interfaces of gapped one-dimensional systems where phases with different topological character meet due to an interplay of spin-orbit coupling, proximity-induced superconductivity and external magnetic fields. Here we investigate the effect of strong particle interactions, and show that the helical liquid offers a mechanism that protects the very existence of Majorana edge states: whereas moderate interactions close the proximity gap which supports the edge states, in helical liquids the gap re-opens due to two-particle processes. However, gapless fermionic excitations occur at spatial proximity to the Majorana states at interfaces and may jeopardize their long term Majorana coherence.Comment: 7 pages, 4 figure

Orbital multicriticality in spin gapped quasi-1D antiferromagnets

Motivated by the quasi-1D antiferromagnet CaV$_2$O$_4$, we explore spin-orbital systems in which the spin modes are gapped but orbitals are near a macroscopically degenerate classical transition. Within a simplified model we show that gapless orbital liquid phases possessing power-law correlations may occur without the strict condition of a continuous orbital symmetry. For the model proposed for CaV$_2$O$_4$, we find that an orbital phase with coexisting order parameters emerges from a multicritical point. The effective orbital model consists of zigzag-coupled transverse field Ising chains. The corresponding global phase diagram is constructed using field theory methods and analyzed near the multicritical point with the aid of an exact solution of a zigzag XXZ model.Comment: 9 page

Local Magnetization in the Boundary Ising Chain at Finite Temperature

We study the local magnetization in the 2-D Ising model at its critical temperature on a semi-infinite cylinder geometry, and with a nonzero magnetic field $h$ applied at the circular boundary of circumference $\beta$. This model is equivalent to the semi-infinite quantum critical 1-D transverse field Ising model at temperature $T \propto \beta^{-1}$, with a symmetry-breaking field $\propto h$ applied at the point boundary. Using conformal field theory methods we obtain the full scaling function for the local magnetization analytically in the continuum limit, thereby refining the previous results of Leclair, Lesage and Saleur in Ref. \onlinecite{Leclair}. The validity of our result as the continuum limit of the 1-D lattice model is confirmed numerically, exploiting a modified Jordan-Wigner representation. Applications of the result are discussed.Comment: 9 pages, 3 figure

Roadmap to Majorana surface codes

Surface codes offer a very promising avenue towards fault-tolerant quantum computation. We argue that two-dimensional interacting networks of Majorana bound states in topological superconductor/semiconductor heterostructures hold several distinct advantages in that direction, both concerning the hardware realization and the actual operation of the code. We here discuss how topologically protected logical qubits in this Majorana surface code architecture can be defined, initialized, manipulated, and read out. All physical ingredients needed to implement these operations are routinely used in topologically trivial quantum devices. In particular, we show that by means of quantum interference terms in linear conductance measurements, composite single-electron pumping protocols, and gate-tunable tunnel barriers, the full set of quantum gates required for universal quantum computation can be implemented.Comment: 23 pages, 8 figure

Universal low-temperature crossover in two-channel Kondo models

An exact expression is derived for the electron Green function in two-channel Kondo models with one and two impurities, describing the crossover from non-Fermi liquid (NFL) behavior at intermediate temperatures to standard Fermi liquid (FL) physics at low temperatures. Symmetry-breaking perturbations generically present in experiment ensure the standard low-energy FL description, but the full crossover is wholly characteristic of the unstable NFL state. Distinctive conductance lineshapes in quantum dot devices should result. We exploit a connection between this crossover and one occurring in a classical boundary Ising model to calculate real-space electron densities at finite temperature. The single universal finite-temperature Green function is then extracted by inverting the integral transformation relating these Friedel oscillations to the t matrix. Excellent agreement is demonstrated between exact results and full numerical renormalization group calculations.Comment: 26 pages, 14 figures: updated version including new a section and figure comparing exact results to finite-temperature numerical renormalization group calculation

Urban Stream Buffer Kawasan Sempadan Sungai Bailang Di Kota Manado

Sungai Bailang merupakan salah satu sungai besar di Kota Manado, makin pesatnya kebutuhan ruang dan ketersediaan ruang yang tidak sebanding, sehingga menyebabkan terjadinya konversi penggunaan lahan yang tidak sesuai dengan peraturan yang ada. Hal ini menyebabkan banyak ruas sungai yang mulai mengalami penyempitan (bottle neck) dan semakin meningkatnya indensitas penggunaan lahan. Oleh karenan itu perlu dilakukan penelitian untuk mengetahui kawasan yang dapat dijadikan daerah Urban Stream Buffer (USB). Tujuan penelitian ini untuk mengidentifikasi kondisi eksisting penggunaan lahan pada kawasan sempadan sungai Bailang, mengidentifikasi kesesuaian lahan pada kawasan sempadan sungai Bailang berdasarkan 3 zona USB, dan merekomendasi USB kawasan sempadan sungai bailang. Penelitian ini menggunakan metode penelitian deskriptif kuantitatif dengan metode analisis sistem informasi geografi dan pengindraan jauh menggunakan bantuan perangkat lunak ArcGis. Hasil penelitian berdasarkan kondisi eksisting penggunaan lahan sempadan sungai bailang terdapat 5 jenis penggunaan lahan yaitu; penggunaan lahan perkebunan, penggunaan lahan permukiman, penggunaan lahan semak belukar, penggunaan lahan tanah kosong dan penggunaan lahan tegalan/ladang. Adapun kesesuain lahan pada sempadan sungai bailang berdasarkan ketentuan 3 zona urban stream buffer, terdapat beberapa kawasan yang tidak sesuai dengan parameter 3 zona USB maka perlu adanya rekomendasi agar sempadan sungai Bailang sesuai dengan 3 zona USB. Kata kunci: Urban Stream Buffer; Sempadan Sungai; Sungai Bailang

Juggling Words, Playing Sages: Proverbs and Wise Sayings in Ghanaian Student Pidgin

Proverbs and wise sayings in most cultures, though grounded in anonymity and communal authorship, have often been ascribed to sagacious old people from antiquity. Most studies on Ghanaian pidgin, a fast emerging area of scholarship, particularly Student Pidgin (SP), focus mainly on vocabulary, syntax and grammar, among other features. However, there is a growing body of proverbs in SP discourse which is not attracting interest among linguistic scholars and discourse analysts. This study fills the gap by presenting a sizeable corpus of SP proverbs and wise sayings which are analysed in the sociolinguistic domains in which they are generated, the diverse communication contexts in which they are deployed, taking into account their linguistic and literary qualities. The outcomes show that most of the proverbs are based on existing ones, allude to specific persons and phenomena while maintaining their uniqueness through the contexts of use. We then call for attention to this aspect of SP. Key words: student pidgin, proverbs, contexts, discourse, implication