Magic-angle helical trilayer graphene

We propose helical trilayer graphene (HTG), a helical structure featuring identical rotation angles $\theta\approx 1.5^\circ$ between three consecutive layers of graphene, as a unique and experimentally accessible platform for realizing exotic correlated topological states of matter. While nominally forming a supermoir\'e (or moir\'e-of-moir\'e) structure, we show that HTG locally relaxes into large regions of a periodic single-moir\'e structure in which $C_{2z}$ is broken, giving rise to flat topological bands carrying valley-Chern numbers $C=\pm(1,-2)$. These bands feature near-ideal quantum geometry and are isolated from remote bands by a large gap $E_{\mathrm{gap}}\sim 100$ meV, making HTG a promising platform for experimental realization of correlated topological states such as integer and fractional quantum anomalous Hall states in $C=1$ and $2$ bands

Enantiospecific Synthesis of 1,3-Disubstituted Allenes from Propargylic Carbonates through a Borylation-1,2-Elimination Process

An array of enantioenriched vinyl boronates bearing an allylic carbonate moiety have been prepared through selective hydroboration of propargyl carbonates. Treatment of these vinyl boronates with TBAF in THF affords enantioenriched 1,3- disubstituted allenes through a novel 1,2-anti elimination in good yields and high enantiospecificitiesWe thank MINECO (CTQ2016-78779-R) and MICINN (PID2019-107380GB I00) for financial suppor

Helical trilayer graphene: a moir\'e platform for strongly-interacting topological bands

Quantum geometry of electronic wavefunctions results in fascinating topological phenomena. A prominent example is the intrinsic anomalous Hall effect (AHE) in which a Hall voltage arises in the absence of an applied magnetic field. The AHE requires a coexistence of Berry curvature and spontaneous time-reversal symmetry breaking. These conditions can be realized in two-dimensional moir\'e systems with broken $xy$-inversion symmetry ($C_{2z}$) that host flat electronic bands. Here, we explore helical trilayer graphene (HTG), three graphene layers twisted sequentially by the same angle forming two misoriented moir\'e patterns. Although HTG is globally $C_{2z}$-symmetric, surprisingly we observe clear signatures of topological bands. At a magic angle $\theta_\mathrm{m}\approx 1.8^\circ$, we uncover a robust phase diagram of correlated and magnetic states using magnetotransport measurements. Lattice relaxation leads to large periodic domains in which $C_{2z}$ is broken on the moir\'e scale. Each domain harbors flat topological bands with valley-contrasting Chern numbers $\pm(1,-2)$. We find correlated states at integer electron fillings per moir\'e unit cell $\nu=1,2,3$ and fractional fillings $2/3,7/2$ with the AHE arising at $\nu=1,3$ and $2/3,7/2$. At $\nu=1$, a time-reversal symmetric phase appears beyond a critical electric displacement field, indicating a topological phase transition. Finally, hysteresis upon sweeping $\nu$ points to first-order phase transitions across a spatial mosaic of Chern domains separated by a network of topological gapless edge states. We establish HTG as an important platform that realizes ideal conditions for exploring strongly interacting topological phases and, due to its emergent moir\'e-scale symmetries, demonstrates a novel way to engineer topology

Cien días vistos por CINEP (No. 79 jul-ago 2013)

El país que no pasa por La Habana. La edición no. 79 de la revista Cien días vistos por CINEP/PPP presenta varios artículos elaborados por el equipo de investigadores y educadores del Centro, donde analizan e invitan a reflexionar acerca del valor y el sentido del diálogo en la construcción de la paz, entendida como cese del conflicto armado y a la vez como proceso de construcción social, política, económica y cultural. Igualmente una paz comprendida como tarea del Estado y de la sociedad en su conjunto. Para esto los artículos plantean preguntas que analizan ¿cómo puede la sociedad civil aportar a un escenario de posconflicto? y ¿cómo la institucionalidad pública y social debe procurar con todos sus recursos, los procesos de reconciliación, de perdón, de búsqueda de la verdad, de no repetición y reconstitución de los tejidos sociales?Índice: Paz. "Posconflicto y política agraria. Una mirada a la experiencias internacionales" por Sergio Coronado y Zohanny Arboleda; "Repensar el diálogo: Una lectura complementaria del papel de la sociedad civil en el proceso de paz" por Diana Chavarro y David Rampf; "Las posibilidades regionales de la paz" por Víctor Barrera. Movimientos sociales. "Protestas en el Catatumbo: ¿y la historia?" por Ana María Restrepo; "Cartas van, cartas vienen" por Mauricio Archila. Derechos Humanos. "Ampliación al fuero penal militar: entre fueros y desafueros" por Mónica Osorio Aguiar. Economía."Para una etapa posnegación Colombia necesita invertir seriamente en condiciones de tipo estructural": Cesar Vallejo por Mónica Osorio Aguiar. Especial. Pronunciamiento de CINEP/Programa por la Paz sobre el Marco Jurídico para la Paz ante la Corte Constitucional por Alejandro Angulo Novoa, S.J