Quantum spin Hall phase in multilayer graphene

The so-called quantum spin Hall phase is a topologically nontrivial insulating phase that is predicted to appear in graphene and graphenelike systems. In this paper we address the question of whether this topological property persists in multilayered systems. We consider two situations: purely multilayer graphene and heterostructures where graphene is encapsulated by trivial insulators with a strong spin-orbit coupling. We use a four-orbital tight-binding model that includes full atomic spin-orbit coupling and we calculate the Z2 topological invariant of the bulk states as well as the edge states of semi-infinite crystals with armchair termination. For homogeneous multilayers we find that even when the spin-orbit interaction opens a gap for all possible stackings, only those with an odd number of layers host gapless edge states while those with an even number of layers are trivial insulators. For heterostructures where graphene is encapsulated by trivial insulators, it turns out that interlayer coupling is able to induce a topological gap whose size is controlled by the spin-orbit coupling of the encapsulating materials, indicating that the quantum spin Hall phase can be induced by proximity to trivial insulators.

Quantum anomalous Hall effect in graphene coupled to skyrmions

Skyrmions are topologically protected spin textures, characterized by a topological winding number N, that occur spontaneously in some magnetic materials. Recent experiments have demonstrated the capability to grow graphene on top Fe/Ir, a system that exhibits a two-dimensional skyrmion lattice. Here we show that a weak exchange coupling between the Dirac electrons in graphene and a two-dimensional skyrmion lattice withN = ±1 drives graphene into a quantum anomalous Hall phase, with a band gap in bulk, a Chern number C = 2N, and chiral edge states with perfect quantization of conductance G = 2N e2 h . Our findings imply that the topological properties of the skyrmion lattice can be imprinted in the Dirac electrons of graphene.

Orbital Magnetization of Quantum Spin Hall Insulator Nanoparticles

Both spin and orbital degrees of freedom contribute to the magnetic moment of isolated atoms. However, when inserted in crystals, atomic orbital moments are quenched because of the lack of rotational symmetry that protects them when isolated. Thus, the dominant contribution to the magnetization of magnetic materials comes from electronic spin. Here we show that nanoislands of quantum spin Hall insulators can host robust orbital edge magnetism whenever their highest occupied Kramers doublet is singly occupied, upgrading the spin edge current into a charge current. The resulting orbital magnetization scales linearly with size, outweighing the spin contribution for islands of a few nm in size. This linear scaling is specific of the Dirac edge states and very different from Schrodinger electrons in quantum rings. By modeling Bi(111) flakes, whose edge states have been recently observed, we show that orbital magnetization is robust with respect to disorder, thermal agitation, shape of the island, and crystallographic direction of the edges, reflecting its topological protection.

Noncollinear magnetic phases and edge states in graphene quantum Hall bars

Application of a perpendicular magnetic field to charge neutral graphene is expected to result in a variety of broken symmetry phases, including antiferromagnetic, canted, and ferromagnetic. All these phases open a gap in bulk but have very different edge states and noncollinear spin order, recently confirmed experimentally. Here we provide an integrated description of both edge and bulk for the various magnetic phases of graphene Hall bars making use of a noncollinear mean field Hubbard model. Our calculations show that, at the edges, the three types of magnetic order are either enhanced (zigzag) or suppressed (armchair). Interestingly, we find that preformed local moments in zigzag edges interact with the quantum spin Hall like edge states of the ferromagnetic phase and can induce backscattering.

Letters from Daniel White to Andrew Hall, March 23, 1799

These two letters, both written on the same document, appear to be White's response to accusations from the father of one of his students at the Medford grammar school. Andrew Hall appears to have accused White of punishing his son too severely. In the letters, White denies Hall's accusations while defending his apparently strict approach to discipline. It is not certain whether both these letters were intended for Hall, or if one was written to another (unnamed) upset parent.

A Mourning Ditty: On the Conflagration of Harvard Hall in Cambridge New England. On the 24th Day of January 1764, [1764]

One-page handwritten copy of "A Mourning Ditty" signed "Philomusus Or A lover of the Muses"describing in a classical style the burning of Harvard Hall. The transcription is signed "Correctly Translated from the Printed Copy, by Peter Thacher." Thacher's translation is of the Latin poem "Threnodia" that appeared on the front page of the Massachusetts Gazette on February 2, 1764.

Prehistoric man, Hall of the Stone Age of the Old World / by Henry Field, Assistant Curator of Physical Anthropology. Foreword by Berthold Laufer -- 8 plates in photogravure and 1 map.

no.31(1933)

The races of mankind: an introduction to Chauncey Keep Memorial Hall / by Henry Field -- Preface by Berthold Laufer -- Introduction by Sir Arthur Keith -- 9 plates in photogravure and 1 plan of the Hall.

no.30(1933)

[Admittatur of Thomas Bartlett Hall], 1840 August 25

Printed copy of an undated abstract of laws and regulations with the admittatur of undergraduate Thomas B. Hall signed by President Josiah Quincy on August 25, 1840. The admittatur identifies Hall as a freshman.

[Certificate of admission of Thomas B. Hall], 1840 August 27

Printed copy of an undated abstract of laws and regulations with the admittatur of undergraduate Thomas Bartlett Hall to the Sophomore class on probation signed by President Josiah Quincy on August 27, 1840. The admittatur identifies Hall as a sophomore.

First Floor, Old Harvard Hall 1667-1764, 1935

Floor plan of the first floor of Old Harvard Hall drawn by H.R. Shurtleff in 1935. Includes the hall, kitchen, buttery, and two chambers

Second Floor, Old Harvard Hall, 1677-1764, 1935

Floor plan of the second floor of Old Harvard Hall drawn by H.R. Shurtleff in 1935. Includes student chambers, tutor chambers, and the library.

Engravings of a plan and an exterior view of Harvard Hall drawn by Pierre Eugène du Simitière, (photographic prints, photostats, and negative photostats), [ca. 1764]

The floor plan details all three floors of Harvard Hall, including its cellars, kitchen, chapel, and library. The items in this folder were reproduced from "The Burning of Harvard Hall, 1764, and its consequences," presented by F. Apthorp Foster at the April 1911 meeting of the Colonial Society of Massachusetts, and published in the Publications of the Colonial Society of Massachusetts, Volume XIV. The floor plan and exterior views were created by Pierre Eugène du Simitière in circa 1764. The original drawings are held in the Pierre Eugène du Simitière collection in the Ridgeway Branch of the Library Company of Philadelphia.

Measures of hall and chapel, [ca. 1800]

This note, likely in the hand of President Willard, directs Mr. [Josiah] Moore and Mr. [John] Walton measure the length, width, and height of the chapel, hall, and library in Harvard Hall. Includes each room's measurements.